My friend Bill is shooting a 62 pound longbow and using 55/75 goldtips and 125 grain heads. I think he stated total arrow weight about 450 grains. His bow is lightening fast, his arrows seem to get good penetration, and they paper test with a perfect hole. I thought his set up was a little on the light side, but he says he has blown through every animal he has ever shot with no problem. He definetely has the speed and said he doesn't need the extra arrow weight for penetration? I have heard a lot of people say they shoot ultra heavy arrows to get penetration, but is Bill right that his perfectly tuned lighter arrows shoot faster, flatter and get better penetration than a slower heavy arrow? Hmmmmm....

An object with a big mass will have more momentum and be able to continue through objects better.

Heavy arrows penetrate better on big bones. Lighter arrows create a much flatter trajectory. Tailor your arrows to your game/shooting style.....luck

Kinetic energy is only part of why an arrow penetrates. If an arrow has blazing speed, It will have higher energy, but if it is light as a straw, it will not have enough momentum to continue on after contacting resistance. Especially something hard like a rib bone. The sharp cut on contact broadhead also lessens the resistance and a perfectly tuned straight flying arrow also helps a great deal with good penetration. On the other hand, a really heavy shaft may not be able to build enough speed to deliver a hard punch and will also have a very high trajectory to reach a distant target. So the trick is getting a balance between speed and mass and making that shaft fly true.

I don't know if Bill will get better penetration with the lighter shafts but it will be pretty close. A .177 calibre hunting pellet weighs only 8.8 grains but at 1350 feet per second it has 35 foot pounds of KE. If it was hard enough to not shatter on impact, it would easily go through a deer's skull, which is pretty heavy bone. KE punches holes in things. Even a grain of sand can go through your skull if it's traveling fast enough and we know that after seeing what IED's have done in Iraq. Heck, even the wadding in a blank can kill if it's close enough to maintain most of the muzzle velocity.

That's right. A heavier calibre bullet will punch through objects such as bone. A lighter bullet moving at high speed will keep richocheting off bone as it passes through an animal.

A light arrow moving at a high speed will do the same. With the right broadhead, it will cut all the way through causing massive tissue damage and bleeding.

In my opinion, 450 grains at high speed should kill almost any animal on the continent. Speed kills more efficiently than mass.

Energy = Mass x Speed So a lite arrow at high speeds can hit as hard as a heavy arrow at low speeds 215 fps 450 weight arrow same energy as 155 fps and 625 weight arrow

It seems like your buddy has the perfect setup! He's shooting straight, fast and with good penetration. I would be concern with such light arrows making increased noise. But if it works for, him great!

WHat no one has said yet on this thread is that a lighter weight arrow looses it's speed much faster than a heavier weight arrow. So out at 30/40 yds the faster of the two arrows is no longer as fast as it was at point blank. Lighter arrows are more subjected to windage adjustments as well. I say to find the heaviest arrow you can shot realitivly flat out to your comfort zone distance wize. No sense having a flat trajectory all the way out to 40 yds if your groups fall all apart at 25 yds. I would want a heavier arrow than the 450 grns for a 62# bow for sure. Any deviation in an arrow that isn't tuned well to the bow would be the biggest detriment you could encounter.

Ryan

Another equation that enters into this is flex. The carbons although lighter are not only a better ballastic coeficient but they are so much stiffer and recover from vibration much faster. All the energy, even if the arrow is lighter is going directly to the point of the arrow instead ob being lost with poor flight or with vibration upon contact with the animal. This concentration of energy on the point of the arrow dramatically increases penetration. This is why tuning is so important. Sounds like your buddy has it all together to me.

Ya' know everybody talks about how much stiffer carbons are than other arrow materials. But, you have to find a method, longer length, addition of weight tubes, heavier points or something to bring the spine to the same place it will be with any other material.

My hunting arrows weigh under 525 gr. Most between 450-475. I use bows from 45-60lbs depending on what Im hunting. Penetration has never been a problem. 2 elk, 2 bears, javelina, a lot of deer, a russian boar, small game. The results have'nt always been pass thru's but usually I do get an exit hole. I rarely use aluminum for hunting anymore, its either carbon or wood.

Last yrs elk I shot with a recurve I made. It pulled 63#, shooting a 525 gr. cedar with a 4 blade magnus b/h I had complete penetration with an exit hole from 33 yds. I found it about 125 yds from the shot.

I did make up a really heavy arrow for an American bison hunt, they were wt'd carbons that were near 700 gr. But the only thing I killed was a jackrabbit on that hunt. I've never used them since.

If he want's to blow his bow up,, that's up to him,, Im not going too...

And if he was shooting a 45# bow, most comments would be he was doing great at 10 grains per pound.

Different ways to kill stuff, sounds like he has found what works for him.

Just weighed my hunting arrows...they're a smidge over 450gr. Not worried in the least about penetration.

All arrows vibrate and flex when shot and when they hit an animal. Carbon just recovers much quicker. That said a heavier arrow with perfect flight is better than a light arrow with perfect flight because it has more kinetic energy and retains its momentum better. If both arrows start out of a bow at eactly the same speed the heavier arrow will have a flatter long range trajectory with higher speed than the light arrow. That is basic if the arrow profile is same.

Just weighed one of my cedars: 495 grains with a 125 grain broadhead. That's 9 grains per pound out of my 55# longbow. Penetration is not a problem and the trajectory is pretty flat.

When you find a bow that is able to shoot a heavier arrow the same speed as a lighter arrow let us know.

Mark the point is that within Stickbow hunting range the trajectory is not as important as the ke

"Energy = Mass x Speed"

No.

Kinetic Energy: KE = MV^2/2

Momentum: P=MV

There are way too many other variables to assume that either equates directly to penetration.

IMHO

- Vic

Newton's theory for kinetic energy is generally used for speeds less than light while Einstien's theory is used for speeds close to light. Both will give you ke but will give you different answers. Neither are wrong as are the many other man made theories to determine work values of a moving object. Any or all of these formulas have some value of scale to aid bowhunters but none are definitive and/or are equal to penetration.

All mathematical lab theories aside and assuming an ethical bowhunter has his archery tackle well vetted and in tune, empirical field data over the decades has proven that a hunting arrow that weighs 9-10 grains per pound draw with a properly designed and properly sharpened broadhead WILL PENETRATE PROPERLY. My personal opinion on using lighter hunting arrows than this is for speed which will gain you a flatter trajectory and nothing more. You may decide to push this to a point but I see no reason for this when hunting with recurves and longbows at the ethical distances we are talking about. Even at longer distances, the heavier arrow will probably carry more momentum and will still out penetrate the lighter one.

later

The problem with relying on kinetic energy as a guide is that it is a square function of velocity relative to mass. That is, a little increase or decrease in speed makes a hudge difference in KE. Momentum, on the other hand,is a linear function of speed and mass. So an increase in either has the same result.

Put it this way - increase the mass by ten percent, without changing speed, and both KE and momentum increase by ten percent. But increase velocity by ten percent, without changiung mass, and KE increases by 21 percent while momentum increases by ten percent.

Sounds good, hey? But wait. DECREASE mass by ten percent, with no change in speed, and both KE and Momentum decrease by ten percent. But decrease VELOCITY by ten percent without changing mass, and momentum declines by ten percent, BUT KE declines by NINETEEN percent.

Momentum, not KE is the mathematical way of quantifying Newton's second law, 'an object in motion tends to remain in motion.' It's harder to stop a heavier object, even if it isn't going as fast.

So? An arrow starts slowing as soon as it leaves the bow. Drag on arrows, in air and on contact with flesh, slows the arrow, resulting in enormous loss of KE. Only adequate momentum keeps the arrow going.

Ever notice how all the KE heads with their wheelbows are shooting tiny little fletches and using hundred-dollar-plus releases and hundred-dollar-plus rests? Because with light arrows anything less than dead perfect tuning and flight results in too-rapid loss of velocity and resultant KE.

Heavy arrows with adequate fletching may not fly as flat, but they forgive, and hit with plenty of momentum to drive a sharp broadhead through the animal.

The problem with that 450 gr arrow is that it only penetrates the ground 2 inches on the other side of a whitetail. Whereas the 650 gr arrow penetrates a full 6 inches on the other side of the whitetail. AND the 650 gr arrow penetrates the ground 2 inches on the other side of a brown bear, but the 450 gr arrow disappears in the brown bear. So what's he hunting?

Ever wonder why there are so many Physics PHD's involved in Trad archery? We need to get out and stick 'em into animals more guys. Screw the math!

Have you ever seen in the movies a guy standing at the castle door with an arrow trying to knock the door open? They used a slower moving log with great momentom. That is taking it to the extream but the theory is the same.

Since when is 450 grains light?

And Adam, your bow won't blow-up shooting 450 grain arrows; if it would, there would have been lots more bows on the trash heap over the years.

My 2016 arrows are around 480 and I sure don't consider them light. There's a point of diminishing returns on both sides..heavy and light.

Amen, George. The problem I see (more so in the wheel bow world) is the notion that KE is all and momentum is irrelevant. And maybe we traditional shooters lean a bit far the other way as well. I'd guess that the returns dininish more as one gets further from some golden mean, say around 9 grains per pound of draw ;-)/2

450 grains is pretty light when you shoot a 70 pound bow. It's all in the beholder.

Pat shot through a HUGE ALASKAN BULL MOOSE with an arrow having only 23 ft-lbs of Kinetic Energy, however his arrow did weigh 800 grains. Bills arrow probably had a bit over 40 ft-lbs of KE or about 75% more KE than Pat's. But guess what??? their arrows would have about the same momentum. Same momentum same results but 74% difference in kinetic energy???

Tonto

If Bills rig is guiet and confortable to shoot then it sounds like he's set. I hope he has a great season and many more to follow.

Good posts from George and Dana.

Your arrow needs K.E. to do anything at all. MOre is better, all else being equal.

Given two arrows with similar K.E., the more massive of the two will be harder to stop, and I believe will therefore penetrate more.

Somebody needs to do a truly thorough, controlled experiment.

Spring how about shooting a dead cow LOL haha

Wow! There are a lot of knowledgeable shooters out there in cyber world! I guess Bill's 450 grain arrow out of a 62lb longbow is just right? He sure shoots it well, and it paper tests perfectly. Very low noise with fur silencers, and game heads on the wall to say he knows what he is doing too! I was just curious what the majority of stickbow shooters thought. Good hunting to everyone!!! Tonto

Wow, do you guys not know about Dr. Ashby's reports? He states unequivocally that momentum is by far the better indicator of penetration....NOT kinetic energy.

Here is a link: http://www.tradgang.com/ashby/Momentum%20Kinetic%20Energy%20and%20Arrow%20Penetration.htm

With lighter arrows he's enjoying a flatter trajectory and is more forgiving of range estimation error. An estimation of plus or minus 3 yards on a 25 yard shot won't hurt him where someone with a heavier arrow might shoot over the back or drop low and hit a leg. He's shooting 7.25 grains per pound which, as he has proven, is lethal. I use 9 1/2 to 10 g/p. It's nothing more than personal preference but 7 1/4 seems light to me.

It's what he's used to so he should leave it alone. The season is already started, it's too late to learn a new arc.

I think most know about the reports Blindmouse.The fact is that his 450gn arrow is blowing through the things he hunts.Unless he just needs a heavier arrow to quiten the bow there really can be nothing to gain by shoot more arrow than what he is useing.Out the other side is the goal and he is already doing that.jmo

"Wow, do you guys not know about Dr. Ashby's reports?"

Yes - but many don't see them as gospel. What mr. Ashby states - what his small sample actually proves - and what it supposedly means to a hunter after white tails here are open wide to interpretation.

Regardless of the "small sample", the sound scientific principles themselves show how momentum rules over kinetic energy. As he states, a tuning fork has a lot of kinetic energy, but is clearly of no use to penetration.

Like I said, many read his "research" with mixed opinions as to what or if mr. Ashby proves anything other then the result he was after.

Well, I think anyone who reads AND understands them will be left with no doubts. There isn't any room for interpretation or opinions when dealing with these types of physics; just as you can't argue against the fact that gravity pulls an apple to the ground, or 1 + 1 = 2. What part of the reports is subject to interpretation, exactly?

You are right - I just don't understand - just as you fail to see there is much left open to interpretation. Others have poked huge holes in his research and methods - but as long as part may be true, many are willing to accept anything the "dr" writes as unquestionable fact(dr of what, by the way?).

Lots of proofs out there that show what some educated individuals say isn't as congruent with fact as it appears to be.

Take the Monty Hall dilemma for example, when it was first printed overe 10,000 responses came in, all saying it was a lie and many sent in by matheticians and staticians with PHD's!

Behind 3 doors are a new car and 2 goats. You choose a door and Monty opens a different door showing you a goat. Now obviously, there are 2 doors remaining, one with a goat and one with a new car, should you change your original guess or stay with it? If you stick with your original choice your odds are still 1 in 3 of being right because you're not taking advantage of the clue Monty gave you, but if you switch you improve your odds to 50/50. Think it through... It's not about education, it's about how well you "see".

As stated above when momentum is reduced to numbers and shown on a scale it's linear. That in itself makes it a better judge.

Also, for the record, even weaker spined carbon arrows recover from paradox and vibration more quickly than their stiffer aluminum or wood counterparts. It's just a superior material if you want quick recovery and less gyration/vibration on impact. It's a fact and nothing can be done about it.

I think I read he is an optomotrist. I'm always a little leary of folks who lean on titles that don't pertain to the subject. I've read his findings and they leave me with way more questions than answers. I think the practical information is useful, but the "scientific" part is so full of holes that I can't take it as fact. I really question the equipment he uses too. It seems he owns the most inefficient equipment on the planet. The energy numbers he cites out of massive bows are not much higher than a good 50# recurve. I don't get that.

oops, Missed!

The big the to consider is Bill says his PERFECTLY TUNED lighter ARROWS, a well tuned arrow will always out penetrate any arrow heavy are light that is not tuned, its more to do with flawless arrow flight if one has spent the time to tune his equipment correctly he can use lighter arrows and heavy arrows something to consider if a 450 grain arrow is heavy enough to hunt with from a 45 lb. bow why would it not be enough from a 62 lb. bow you need to worry more about a well tuned bow and arrow with as perfect as arrow flight as you can get than how heavy the arrow needs to be, 450 grain will Kill anything you are going to hunt if it is tuned to your set up.

Ashby's first report on broadhead performance is informative. The others?????? Who is funding him to traipse around Africa shooting at game. Somebody has to be paying him for these "scientific reports". Sweet gig.

Here's a proof from KT of what I said, how well you "see".

"if a 450 grain arrow is heavy enough to hunt with from a 45 lb. bow why would it not be enough from a 62 lb".

Obviously an unrefutable fact. From 62 pound bow it's going MUCH faster than from a 45 pounder. It's just that with a 62 pounder he could increase his arrow weight and REALLY increase his penetration potential.

By the way NY Yankee...450 grains weighs the same at 70 pounds as it does at 55.. 8^). It still has ample weight for killin North American game.

Once again, we ignore those things that have worked very well in the past and look for some holy grail of penetration. I guess Sigmund Freud would have a theory as well.

Dr. Ashby's report has merit...especially on "large game." We know that a cape buffalo is a little more difficult to penetrate than an elk...Hello! We also should know, that deer are thin-skinned, as are the black bear and most N.A. game.

It's amazing to me that we consider a 255 grain bullet extremely heavy, and a 450 grain arrow extremely light...another Hello!

Jack Howard was unquestionably one of the best bowhunters of the 50's 60's and 70's, taking all kinds of big game in the west. Jack was a proponent of fast arrows and normally shot arrows under 500 grains. Amazingly he got lots of pass-throughs and complete penetration on large game.

End the final analysis, it is good arrow flight that makes for good penetration, whether or not that arrow weighs 450 or 850. Wobbly arrows...even slightly wobbling...are penetration killers. If you shoot well-tuned 850 grain arrows, that's great, as long as you hit what you want to hit. That also goes for 450 grain arrows. They will both get the job done with little effort and will both let short blood trails to follow.

To re-iterate more strongly, you cannot have one without the other.

You NEED sufficient kinetic energy to penetrate game. Period.

If that energy is derived through high speed and low weight, you still have the energy, and KE is the measurement of an objects ability to do work.

The problem is that at high speeds, demons creep in. Drag increases, incremental speed losses cause exponential energy losses. Tuning errors cause the loss of proportionally more energy at high speeds than at lower speeds. On and on.

Basically, I would still like to see what happens to arrows with identical KE but widely different momentum measurements at termination of their flight.

If it was me, Id shoot them through a green hide, then a half inch of ballistic jelly or fresh meat slabs, and through exactly spaced 1/2" by 1/4" slats set like jail bars. This way about half the shots would be through hide and meat, and half would be through hide, meat, and bone. A couple dozen shots should give a pretty good sample at each range for each arrow.

I'd place a chronograph on the FAR side of the target and measure momentum and KE differences at that point. The basis of my thinking is that I'm not interested in what the numbers say in front of the bow. What happens after the arrow has gone 10, 20, 30 yards? What happens after the first inch of penetration? HOW MUCH LUNG AM I GOING TO GET???? I have no doubt that the KE will differ a great deal between those two arrows at that point.

All that said, I see nothing wrong with good flight and good penetration your friend is getting.

To me, this picture indicates a very good test of KE. Here is the link to the article if anyone is interested http:// www.martinarchery.com/faq/facts.php It is a consistent, repeatable result, something you won't find from shooting into an animal. If I wanted to prove my rig was adequate for a certain animal, I'd shoot into said animal's carcass a number of times, but I wouldn't use that for a test of my broadhead or arrow's efficiency versus another. If I was going after Asiatic buffalo, I'd definitely up my arrow weight, no question. It has slightly more KE and will be more efficient on the very heavy bone that you are inevitably going to encounter on such an animal. For North American, and even most game in Africa, I want the arrow that will increase my accuracy and help me avoid that narrow ridge of bone in the shoulderblade that is so difficult to penetrate, something I wouldn't bet on my arrow penetrating anyway. A certain weight and speed arrow helps my accuracy, even at 20 yards! I hear people say it doesn't matter at stickbow distances, but it does! Besides, my goal is to advance and extend my effective range, and give myself that edge at unmarked yardages.

Honestly, I don't think most traditional guys' gear is tuned to perfection. My arrows MUST perfectly bareshaft at 40 yards, or they won't go into my quiver. Simple as that. That is where I believe most penetration problems come from. I'd rather have my perfectly flying 450 grain arrows than a 700 grain arrow with a slight amount of mistune for penetration, all other things aside. I have seen the results of a perfectly tuned lighter arrow from many people, even on this very site in the form of pictures. They are very efficient on the bones of non-armor-plated game ;) People's success with these type of arrows, even on the bones (such as elk ribs and shoulders) so many people seem to worry about is enough for me.

JMO fwiw

Craig

upping the weight of your arrow won't affect your KE,,, just your arrows speed. the momentum factor will change though. i wouldn't assume that most traditional bowhunters don't tune their arrows well,,, traditional bowhunting sucess rate is actually very good from what i've read.

My arrows MUST perfectly bareshaft at 40 yards, or they won't go into my quiver.

I'd like to see that, So you don't need fletch. Thats novel. Hunting arrows with no fletch. Seriously I'd like to see a perfect arrow flight at forty yards, thats 120 feet with no fletching.

I'm not saying they're not tuned well, I'm saying not perfectly. A heavier arrow will mask a tuning issue better than a light one (just like an inefficient bow will), and it will penetrate better than a lighter one when both are improperly tuned. They also mask form problems better.

KE actually goes up as arrow weight goes up, but not very much. All I know is I sure wouldn't be happy with the arrow tune the trad guys I personally know have.

In my opinion, it takes a good amount of momentum to break through a tough, or armored object (such as a cape buffalos ribs), which is why you don't want to use a light arrow on them. But I think that KE has a significant place in the actual depth of penetration. Elk and deer ribs ain't buff ribs, and I'd rather attempt to avoid that shoulderblade ridge than have an arrow that I am less accurate with that MAY go through it. Ribs on the stuff I shoot at, I'm not worried about though.

"I'd like to see that, So you don't need fletch. Thats novel. Hunting arrows with no fletch. Seriously I'd like to see a perfect arrow flight at forty yards, thats 120 feet with no fletching."

That's exactly what I'm talking about. Come over to my place and I'll show you a bareshaft that impacts perfectly at 40 yards with no fletching! I try to get it flying straight, but where it impacts is most important. I do need fletch for broadheads (though I have got a broadhead arrow to impact correctly at 40 yards with no fletching, NOT RECOMMENDED and I don't plan on doing it again), and when there's wind. They're are plenty of reasons for fletching, as everyone knows. Tearing it off (I replace it with weighed tape so it makes up for the lost fletching) reveals the mistune you can't see.

BTW, I'm not saying you need to bareshaft to 40 yards. I do like to though. I would say do it to at least 25-30 yards. I think tuning is an underated and essential component to penetration.

Good points that you made Arrow4christ. Its unbelievable that folks still dont know what bareshafting is. Or dont realize that a bare shaft properly matched to a bow can be shot without fletching a long range.....and yes it can be done at 40 yards. I've seen olympic contenders shoot bare shafts 70 meters and hit bulleyes. A well tuned light arrow will out penetrate a poorly flying heavy arrow anyday of the week.

A4C: true about KE's changes with added arrow mass,,, very little. here's some good reading by pete w from a while back:

I wouldn't hesitate to use that setup for Elk or moose. just don't take stupid shots. I would go up in arrow weight ,but I like heavy arrows. The KE does not change much when we change arrow weight. Normaly about 1FT/LB.so for the KE fan club there is no reason to shoot light arrows .But look at the momentum changes as we increase weight. It goes up a lot. As for increasing draw weight, I have 60# bows that have less performance than the bow you have,but I guess because they are 60# they should be better? I think not. Arrow speed and weight are the factors that are important. The numbers below are from a 60# recurve I have , and I am puting them here to show how arrow weight affects KE and Momentum.Note that KE is virtualy the same as weight goes up, but look at the Momentum values.

[email protected]@20yds..momentum@20yds

ICS400.......404........210.....39...36.................200.................357 ICS340.......428........205.....40...36.................196.................371 CEDAR......460........190.....37...34.................181.................370 FIR.............500........180.....36...33.................173.................382 ALUM........505........180.....36...33.................173.................386 ALUM........535........173.....35...33.................167.................395 SPRUCE....608........167.....38...35..................161.................435 SPRUCE....615........166.....38...35..................161.................437 SPRUCE....646........162.....38...35..................161.................450

I'm not convinced that bare shafting a field tip arrow for perfect flight out to 40yds has anything to do w/ perfect flight from the same shaft w/ a hunting broadhead. How an Olympic target archer bare shaft tunes a target arrow has nothing to do with flight of a hunting arrow. Opinions differ and each to his own; but my 33yrs of personal experience bowhunting with self bows, long bows and recurves has me in agreement with the experience offered by Kelly found in (Kelly's Tips at Arrows by Kelly):

"Since we are bowhunters and use broadheads while hunting, we tune our equipment with broadhead tipped arrows. Once we find the perfect flying broadhead tipped arrow, we than can use any other type of point for practice with no ill effects. It has been common knowledge for many decades that an arrow tipped with field points, which flies straight and true, may or may not fly true with broadheads. For years, bowhunters were taught to shoot all their broadheads to weed out the “flyers”. Conversely, we know that an arrow which flies true while broadhead tipped will always fly true with any other type of point, be it field, Judo or blunt.

It makes absolutely no sense to go through all that is necessary getting good arrow flight with field point tipped arrows, or for that matter, bare shafts and then still not know for sure whether broadheads mounted on these same arrows will fly true. Rather, we choose to eliminate this difficult, lengthy effort and waste of time, and tune with equipment exactly as it will be used in the field, Bowhunting."

I'll close by saying I further find any claim/statement that a 6-7grain per pound max draw weight carbon arrow automatically has perfect flight while a 9-10grain per pound max draw weight hunting arrow automatically has poor flight ... this is without basis and is fiction, not fact. I'm of the opinion you need about 40pounds or so of draw weight to hunt big game and you need at least 6-7grains per pound max draw as most bows by design cannot handle anything lighter without risk of damage. I find 9-10 grains per pound max draw ideal for me.

later

How many bare shaft with a broadhead? 'nuff said.

Daddy Bear, my thoughts exactly, nice post.

KODIAK, What does that have to do with anything? Bareshafting with a broadhead puts wings on the wrong end of the arrow. Bareshafting perfectly with a fieldpoint will get your broadheads to fly perfectly with fletching. Daddy Bear, I never said you couldn't get a heavy arrow flying perfectly. Taking the fletching off WILL reveal arrow spine issues you can't see when you don't bareshaft. If it's weak it will show. If its stiff, again it will clearly show. 808, I realize that momentum goes up drastically as arrow weight increases and KE stays almost the same. I just think that as long as your reasonable, with a perfectly tuned arrow, you can shoot either with great penetration. Craig

Do you shoot at game with broadheads on or don't you Craig?

I'm thrilled you think you can bare shaft "perfectly" at 40, but read Daddy's post again and maybe it'll become more clear to you.

Heavin forbid we get our hunting arrows flying as well as well tuned target arrows. An no their not the same and the game is not the same. But bareshaft tuning is the same for me hunting or not. I like straight flying arrows......they penetrate better too!

Daddy Bear, I agree 100%...If a person is going to shoot broadheads, they might as well start with them up front cause they'll still need to fine tune them. Tuning with bare shafts or broadheads tells you the exact same thing only tuning with wide BH's will result in a better tune. I only bare shaft if I'm setting up shafts I'll only shoot target with and no broadheads.

The KE thing....The ONLY thing a bow puts out is KE...The shooter decides how they are going to use that KE....Like 808Grapplemonkey pointed out, a bow's KE doesn't change significantly with arrow weight..It's horsepower is fixed....What isn't fixed is how fast we use that horsepower. Just like low gear in your truck, you can do a lot more work with XXX amount of horserpower if you use it slower.

Anyone that thinks a 60# bow is more powerful then a 40# has to know KE is important since that is the only thing a bow gives us. The KE out of a bow only tells us the bows potential. It's up to us to use it correctly. A set up closer to optimum out of that 40# bow will/can out penetrate/perform a poor set up out of the 60#. It's usually not an issue with thin skinned game as others have pointed out. Saying that in other terms is we can do a lot of things WRONG and still be successful. It's when we crowd the edges will those mistakes show and usually at the critters expense.....O.L.

Have you ever actually bareshafted an arrow? Either of you? I suggest you try. I still don't understand where the debate is here. I mount broadheads on my arrows and they fly perfectly true after bareshafting.

How much penetration does one need if a 400 grain arrow exit the other side of the animal is this not enough I kill deer, wild hogs every year with a 52# DAS recurve with a 450 grain arrow that is tunned to the best of my ability and never have a problem my freezer stays full of game meat year round maybe the animals are just getting harder to kill, but just last weekend I sent my light 450 grain arrow thru the lungs of a buck and he ran 25 yards and died but Maybe if I shot him with a 650 grain arrow he would of fell in his tracks.

are you seriously asking O.L. if he ever bareshafted?

My bowyer helped me bareshaft tune my Gold Tip 3555's to my new recurve. Once they flew true, centered equal weight broads flew perfect w/ fletching of course. My bow is 46# @ 28". Arrows are 540 grains total. Chrono in the 190's. Also, bareshafting improved my accuracy a ton.

808, the question was directed at KODIAK and John, not OL.

KT said: "I'm of the opinion you need about 40 pounds or so of draw weight to hunt big game and you need at least 6-7grains per pound max draw as most bows by design cannot handle anything lighter without risk of damage. I find 9-10 grains per pound max draw ideal for me."

We can argue theories and values all day, but this is the best APPLICATION that I have heard.

Until someone can post a chart showing a minimum acceptable arrow weight and speed of arrow flight for each game species, this is the best guideline that I know to follow.

Jim

I've never actually heard anyone try to make the case that bareshaft tuning is a bad thing before. But I suppose today's a new day. :)

Tonto, I think your friend Bill has figured out a thing or two that others are still stumbling around with.

My apology... Daddy Bear said it not KT.

Jim

I'm still haveing a problem here. Now you may find this strange but in 50 plus years of bowhunting and owning a proshop and shooting professionally for three different Major companies I have never seen anyone that could get a clean enough release with fingers to do what you are talking about. My release with fingers is 2 to 3 fps slower than with a mech. release and I thought it was about as good as it could get. In fact when I went from bowhunter class to unlimited my scores did not dramatically improve and many times I shot higher scores in bowhunter class than were shot in the unlimited classes.

I have always paper tuned but never even considered bareshafting at the ranges you guys are talking about.

Tell me if an arrow has not overcome torque after ten yards what is the point of extreme range bareshafting. If it shoots a perfect hole throug paper with your broadhead attached then what else do you have to do? I know I just don't get it so please explain.

Arrow4Christ

Yes I have bareshafted arrows. Started almost 25 years ago. I am in agreement with you on bareshafting. Read my post again and you will see.

I am sorry John, I made another mistake in my post. It was meant for KODIAK and Daddy Bear. Darned if i ain't the clumsiest guy! LOL

BTW I agree 100% with your last post on target vs. hunting tuning.

now there's a target vs. hunting arrow tuning issue?

"But bareshaft tuning is the same for me hunting or not. I like straight flying arrows......they penetrate better too!"

I right with ya Arrow4christ!

Well I'm going to try it LOL here goes some lost shafts I bet

sixby, Good luck! It will take some time probably to get them flying good and straight, but it will be worth the effort! Craig

Sixby, "I'm still haveing a problem here. Now you may find this strange but in 50 plus years of bowhunting and owning a proshop and shooting professionally for three different Major companies I have never seen anyone that could get a clean enough release with fingers to do what you are talking about."

First there are 2 kinds of bare shaft tuning...The "kick" method is nothing more then paper tuning where you are concerned with shaft angle either in flight or sticking in the target. I agree with you...This is so dependant on "form" to be all but useless for most folks.

The other method is the "planeing" method and it works by comparing the relatioship between fletched and bare groups and works very well. Poor form makes your groups bigger, that's all. It will NOT make fletched arrow go one place and bare or wide broadheads go another. If I shoot bare and fletched shafts at a target 30, 40, or 90 yards away.....I could care less if the shafts are sticking in the target "straight" or "look" straight in flight as long as they are grouping with the fletched shafts. Fact is the best tuned equipment with the best shooters can't shoot a shaft "straight" 90% of the time so why look at it. It's a problem that can't be fixed using tuning methods and if you try, you'll be over spined 99% of the time.

If you shoot at a target with a bare shaft or wide BH..What ever the bare shaft or wide broadhead does, all of your arrows are doing the same thing, just not as noticeable.

The biggest mistake folks make is trying to mix the 2 methods. It's a recipe for mass confusion.....O.L.

"Fact is the best tuned equipment with the best shooters can't shoot a shaft "straight" 90% of the time so why look at it. It's a problem that can't be fixed using tuning methods and if you try, you'll be over spined 99% of the time."

I did it with my compound bow and mechanical release...

If you're talking about penetration of gelatin or critters, arrow speeds are rather low compared to bullets. Still, we can approximate the penetration in the same manner:

pen = (mass x square root of velocity)/constant

IIRC, some Native American hunters used small diameter arrow shafts to promote penetration. As slow as arrows impact, using razor sharpe broadheads will greatly improve penetration over blunter points.

"The KE thing....The ONLY thing a bow puts out is KE...The shooter decides how they are going to use that KE....Like 808Grapplemonkey pointed out, a bow's KE doesn't change significantly with arrow weight..It's horsepower is fixed....What isn't fixed is how fast we use that horsepower. Just like low gear in your truck, you can do a lot more work with XXX amount of horserpower if you use it slower."

This is a specious argument akin to ping pong balls and golfballs thrown into snowbanks. There are enough scientific resources available online to find out what's wrong with this, so I trust those who really want to find out the truth can do their own research on it. And, of course, those who want to believe this argument is a really awesome argument can just accept that it is regardless of scientific support or lack thereof. And those that don't care... well, nevermind. :)

Rolin, I was just running some numbers through that equation, and it doesn't seem to work for what I know from experience.

The other day I was shooting my longbow alongside my compound shooting buddy.

His arrows always outpenetrated mine by a large amount....often burying to the fletching in the target, while mine left a good foot or more of arrow hanging out.

His numbers: 420gr arrow at 300 fps My numbers: 650 gr arrow at 150 fps.

Using your equation, my arrows should have penetrated more, but they did not (not even once over many dozens of shots).

Blindmounse, your physical results are in line with what the respective KE indicates they should be. 83.96 for his setup and only 32.48 for yours. His will penetrate much deeper every time. Models that try to prove mass and velocity are equally weighted in regard to penetration don't work. They are fundamentally flawed because KE is the energy of motion and doubling velocity (motion) quadruples the Energy. Catch a baseball going twice as fast and it hits your glove 4 times harder.

blindmouse,,,your freinds bow puts out twice the KE yours puts out,,,his 83.96-yours 32.48. no matter how heavy your arrow is the outcome will always be the same. what kind of compund does your friend shoot? those are some good numbers.

Not sure what kind of compound he shoots...I do know it is the latest model of something that he traded in a Switchback for...and he likes this new one much better.

Prolly a Drenaline. Quick bow and quiet too.

Blindmounse,

Your Mom = 97,500-grain-ft/sec His Mom = 126,000-grain-ft/sec

Assuming a 29" shaft less five inch fletch & nock, he got 24" of penetration.

97,500/126,000 = .7773, so on the momentum basis you should have .7773*24 = 18.5 inches of penetration.

29-18.5 = 10.5" hanging out, give or take a variance in arrow diameter, and the fact that the faster arrow has more drag in the target; Id say you have a tuninig problem.

Lets see some one do that using KE numbers.

canopy

Canopy, the Blindmouse reports results similar to other reports, including testing done by Martin Archery. It indicates that KE is the best predictor of penetration. As Einstein said... if the facts don't fit the theory, change the facts.... so Blindmouse must have a horrible tuning problem. :)

I'm not so sure. I do believe the arrow with the higher momentum and mass penetrated the deepest in all the vetted test I've read. I'm fairly sure most emperical data supports this and most data indicate that ke values are unreliable as a predictor of outcome penetration.

The most extensive report on this topic comes from Dr. Ashby’s Broadhead and Arrow Lethality Study. I’m unaware of any field testing that is as well controlled, documented and vetted as his.

As to kinetic energy and how it relates to outcome penetration:

“The study continues to examine kinetic energy, momentum and arrow mass, and how they relate to outcome penetration in tissues. Though a highly complex subject, these, along with an understanding of the resistance forces involved, are the most important aspects of the study; the basic forces determining an arrow’s ability to penetrate real tissues. As has been the case with prior data, no correlation trend between arrow kinetic energy and penetration can be established. To clearly bring this lack of relationship to the reader, Graph 7 presents the raw impact kinetic energy and penetration data for the 364 buffalo shots. The range of impact kinetic energy is from 23 ft.-lbs. to 94 ft.-lbs. If anything is striking about the data it is the randomness.” - (Ashby Report)

As to how momentum is relevant as a predictor of outcome penetration:

“A relevant relationship exists between mass and momentum as ‘predictors’ of outcome penetration.” - (Ashby Report)

Daddy Bear

Daddy Bear, Dr. Ashby's second report demonstrated findings contradicting those of the theory in his first report, which caused him to then conclude that it must be high FOC of the lighter arrows that cuased penetration to remain very consistent with the KE and not constant at all with the Momentum. I wasn't surprised by those results at all and believe that his premise that momentum is key was incorrect in the first report and that adding an exception to that rule via high FOC simply compounds the error.

Dr. Mark Timney wrote a very good article featured on Bowsite long before the 2nd Ashby report threw the first into question. Even the good Doctors can't agree on this, so it's no wonder we don't. :)

http://www.bowsite.com/bowsite/features/practical_bowhunter/penetration/index.cfm

Taking all the findings into consideration, there is a striking correlation between the KE and the distance of penetration in Dr. Ashby's chart. Notice that the difference in arrow weights effectively used for Buffalo range from 637 to over 900 grains - a difference of over 40 percent. The momentum, as we would expect from such a range varies over 20 percent. The KE and Penetration, however, are the two most closely related numbers in the chart.

AWright, but I still see both sides of the argument comparing apples and oranges.

In my mind, the REAL question is more like this:

Viz. Blindmouse and his heavy arrow vs. his compound buddy.

Penetration differed because energy (KE) differed. Fine. Agreed. Obvious from both the numbers and the experience.

What I want to know is, what would happen if the 650 gr arrow and the 420 grain arrow were shot at speeds such that their calculated KE was EXACTLY the same.

The article on the Martin test doesn't answer this question well enough for me.

It irrelevant to compare heavy and light arrows with different KE. Two variables are too many for this kind of test.

PapaBull,

Given that his 650-grain arrow most likely has a larger ballistic diameter (and target resistance); he should have somewhat greater than 10.5" of arrow hanging out (he says a foot or more 18"??).

The point was using MOMENTUM ALONE, the amount Penetration can be estimated by simply using a ratio of the two arrow's momentum.

I say "Only estimated", because of the difference in arrow shaft diameter, shaft surface drag in target, variation in BH style or blade sharpness and other variables soak up momentum differently as the arrow(s) enter(s) the target.

canopy

Blindmouse,

The m*V^0.5 equation was obtained by researchers primarily working with pistol bullets and small spheres (such as shotgun pellets). The actual empirical equation they found was more like m*ln(V) but I use the former equation for simplicity. Carroll Peters' book "Defensive Handgun Effectiveness" has a good explanation of this topic.

How well does the heavy arrow stabilize at 150 fps? Could the arrow be yawing at impact? Are both weights of arrows using the same point?

Just for fun, think about this...

Your friend's arrows had about the same kinetic energy as a two-inch barreled .22LR or .25ACP pocket pistol. Which would penetrate farther or do more damage, the tiny bullet or your friend's arrow?

Canopy, you can use anything you want to estimate penetration but if you are using an inappropriate algorithm, you will have an inaccurate estimation just like in this case.

Apply your algorithm to the results in the Ashby chart I posted above and you'll see it won't work there, either. KE and Penetration are much more closely related than ME and Penetration. And this is from Dr. Ashby's own report.

Rollin, you ever wonder how much damage a .25ACP pocket pistol could actually do if it shot razor sharp broadheads instead of flat tipped lead balls?

Ran a few numbers..... a 125 grain broadhead going 550 feet per second carries 83.98 foot pounds of energy, exactly what Blindmouse's friends arrow had.

Ever wonder what a 125 grain broadhead flying all by itself at 550 fps would do to something it hit? I don't think that there's much that it wouldn't cut a hole all the way through with that kind of speed and KE. 125 grins of Razor sharp steel blades... 1-1/16" wide.... 3:1 cutting ratio.... travelling at 550 fps!!!! Now THAT'S nasty!

anybody see many people bowfishing with really light arrows?........

wonder why they use those 1000 +gr fiberglass arrows :^)

probably because light arrows don't penetrate several feet of water very well and still retain enough momentum/KE (you choose which one you like) to punch through fish.......

KE is probably pretty close with a 1000gr arrow as it is with a 350gr arrow off the same bow right?

most tissue is primarily water right?

so why don't people use light arrows for bowfishing or better yet, why don't the arrow manufaturers make light fishing arrows?........... i'm guessing lack of penetration and momentum :^)

I have shot 4 deer (in the kill zone) with arrows weighing less than 480gn where the penetration was so bad they were'nt recovered. I could see the arrow as they ran confirming the location and poor penetration. They were tuned very well. None were carbons. Since then I have used arrows no lighter than 650gn and never had another penetration problem.

Shapeshifter, you got suckered into one of the big fallacies of the "heavy arrows is better" theory; that animals are primarily water so it must be like shooting through fluid. WRONG. Flesh isn't fluid. Water is fluid. Air is fluid.

Besides, I've shot fish that I've stuck to the bottom of a pond in water chest deep with a cedar arrow. Heavy arrows are important for bowfishing more because they are more suitable for towing a line that is peeling off a fishing reel with a fairly slow, manageable speed.

You also want a very tough arrow because you're going to have to handle a fish by it and you want it to survive shots into the rocks. Been there; done that. Solid fiberglass is the ideal solution.

Now there is a scientific basis for a formula of drag that increases resistance 4 fold for a 2 fold increase in speed and it is, indeed, drag that affects a fishing arrow as soon as it hits the water and starts moving through it. Once again, that's because water is FLUID. Animal flesh is not fluid no matter how much water it contains so the force of drag is not operative.

So now you know why the fishing arrow argument is a non-starter, Gino, even though I know you thought it sounded like the best answer you ever heard regarding this. :)

still the best analogy i have ever seen used.

i prefer to do my research on live game not from my PC......

heavy arrows have always performed better on animals for me than light ones...... plain and simple.

by the way, it is OK for people to have a different opinion than you robert...... i just feel bad for ya because you seem to take so much time out of your personal life to try to prove YOUR point...... just go hunt and have some fun.... it is good for ya!

It's a great analogy if you don't mind supporting your personal viewpoint with specious arguments.

Relax, Gino. It's cool. Someone has to balance this stuff so it's not all one-sided boviating by guys with really bad analogies. :)

So Gino what is your effective range with those fishing arrows on big game? Most people will shoot arrows within 200gr of each other out of the same bow and I don't think you are going to see that much differance in penetration between 450gr and 650gr out of the same bow. The only time you should really use the super heavy arrows is if you are going after really big animals like buffalo. Deer you can shoot through with just about anything and elk I wouldn't shoot them with anything less than 450gr arrow out of a 55# bow.

Something that is 70% water is not a solid, no way you can make that argument which what you seem to be saying. Lungs, skin, flesh, blood ect are all at least semi-fluid to varying degrees, so I believe Shapeshifters argument has some validity.

A block of wood is a solid. A lung is not a solid, you can squish it between your fingers. That indicates some degree of fluidity.

That said, I still use pretty light arrows (460 grains) 'cause they get the job done. ;^)

Kodiak, Ice is 100 water. Is it solid?

Fluid does not mean "not solid". Air is fluid. Water is fluid (until it freezes). Oil is fluid. A sponge can be smashed between your fingers and it's not at all fluid.

Fluids share the properties of not resisting deformation and the ability to flow. Animal flesh, whether it's lungs or tough neck muscles, do not flow and do resist deformation. They share neither characterstic of a fluid and in order to actually BE fluid, BOTH characteristics must be present.

Dropping a lead ball into any fluid that is less dense than lead will result in the lead ball moving through the mass and resting on the bottom. If it's a fluid more dense than lead (like mercury), it will float.

We cannot assume that water content determines fluidity. Animal flesh may be over 90% water and it is still not fluid. It won't pour. It won't flow. You can't dip a ladle into an animal and pull it out filled with backstraps.

See this link to a more robust definition of "fluid". http://www.windows.ucar.edu/tour/link=/physical_science/physics/mechanics/fluids.html

kodiak- that was not mine, it was just a post that i saw JRW make some time ago. however you are right, i think it does have some validity. problem is, some people just can't seem to agree to disagree and get worked up over others not buying into what they think is right....... i say if it works for ya, use it and who cares what others say....... if it doesn't work, learn from your mistakes and move on.

chris- nah, just throwing out some food for thought..... i shoot arrows in the 550-650gr range(35 yards is point and my max range that i'll shoot with this year's 610gr arrows) and in my own experience with elk have seen a difference in pentration with arrows from my longbow/recurves with arrows that were in the 630gr range vs. my compound in the 430gr range with similar or the same broadheads (never had an exit wound with the compound)...... i know some have had great luck with light arrows, just figure i'd stick with what has worked for me the best. i agree with you that just about anything will punch through a deer with a well placed shot.

why not less than 450gr. and 55# on elk? have you had a bad experience on elk with less? just curious..... i always like to hear fellas experiences (regardless of the outcome) on elk to see what has and has not worked...... guys that have had hands on experience with the topic at hand are the ones that i like to learn from and/or with.

Gino, never had any experience with elk yet. I usually adjust my arrows for the game I am hunting. If I am going after deer like this year I used 435 gr arrows and 56# DAS with good results that is the lightest I have ever used. Last year in Africa I used 560gr arrows out of a 60# bow with excellent results. I would probably go with that set up going after elk (if I ever get drawn for the place I like to hunt). I like the middle of the road for most things just like in politics I am not left or right but right in the middle. I agree use what has worked for you in the past and gives you the most confidence that will bring home more game than anything I know of.

cch, I've used arrows from 380 to 420 grains on Whitetails out of my 55# Desperado with perfect penetration. I don't have experience with elk yet, either, so I let others discuss that.

Gino... it's OK for you to disagree. I laid out what's wrong with the analogy you provided. I cited the facts to support my explanation and gave references to support the facts. And if, in light of that, you want to arbitrarily decide to disagree, anyway, I have no problem with that. Are you sure you're not just being a little disagreeable because your analogy didn't hold water?

Papa Bull,

I've tried to follow your remarks/statements you attribute to Dr. Ashby's study, his FOC chart you posted, Dr. Timney's article, etc.

First, the FOC chart has no bearing whatsoever in this conversation over a correlation between ke and penetration. That is a complete separate part of Dr. Ashby's study and you've taken it out of context.

Second, nowhere in his study from empirical data does he assert what you claim that there is a correlation between ke and penetration. One can theorize till the cows come home and it has little value unless it matches empirical data from the field. Dr. Ashby studied just about every available broadhead available over two years on (364)THREE HUNDRED AND SIXTY FOUR KILLS and in nowhere did he find any relationship or correlation between penetration and ke. His very own words from the study are "Does anyone see a correlation? I can find none." Where he did find an absolute clear correlation was with momentum. His own words from the study are "Momentum and penetration correlation is easy to find.

Third, Dr. Timney's article was just that, an article. He rehashed old basic mathmatical data of others based on theory and gave some general broad brushed opinions on this theory. Absolutely nowhere are his words backed up by any empirical data from controlled and vetted field testing.

As I said above, I'm unaware of any empirical data from any controlled and vetted field testing that supports any theory that there is a correlation between ke and penetration so as ke can be used to predict outcome penetration. On the otherhand, such empirical data does actually show a correlation between momentum and penetration so that momentum can be used to predict outcome penetration.

In closing, during my three decades of hunting with basic archery tackle I've found a solid benchmark for penetration as such:

With a tuned bow of the proper draw weight for the chosen game; a proper and sharp BH on the end of an arrow w/ total weight between 9-10gr per pound draw will give you near maxmum penetration for that combination. There is some wiggle room, but going much lighter than this will give you a flatter trajectory only and will not increase penetration. More that likely it will reduce penetration.

Daddy Bear

LMAO!!!!!!

Gary, you and i must have been typing at the same time...... i was laughing about the statement before yours......

Daddy Bear, try following what I said a little harder. It wasn't all that complicated. Maybe if I clear up a few misconceptions for you, that might help.

The "FOC chart" wasn't taken out of context at all. It is only an "FOC chart" because that's what it was named. It's also a penetration chart, a KE chart, an ME chart. If the data is valid, then the data is valid and can be used for a variety of analysis. If the data is correct it's valid for analysis on all data listed.

That chart became "the FOC chart" when Dr. Ashby couldn't explain why the "light" arrows weighing 40% less than others got the same penetration with the same KE despite a notable difference in ME. Dr. Ashby concluded it must have something to do with FOC. A more critical evaluation leads us to see that MO isn't as much of a predictor of penetration as KE is... back in line with the Martin Testing. Back in line with Dr. Timney's explanation of terminal ballistics.

This is the ONLY chart Dr. Ashby provided listing the actual DATA. The rest of his article was just an article rehashing his theory of MO = Penetration and KE = completely irrelevant. And the first chart with actual data blew the theory out of the water.

Well, let's cut to the chase. Now you DO have empirical and vetted data that you've never seen before showing a correlation between KE and Penetration, Gary, unless, of course, you don't feel Dr. Ashby's data is "vetted".

Did you know the first Ashby report was written in an effort to persuade South Africa to remove their "Minimum KE" restrictions citing MO as more important (and more easily attained by stickbow shooters)? Do you think that might have had some bearing on what the study would conclude?

If we're going to discuss this in a rational way, then physics comes into play. The numbers in the chart are subject to anlysis. The principles involved are subject to being evaluated and tested. In other words, "I believe it just because I believe it" or "just because so and so said it" or "because I just know" isn't very effective or compelling. But that's only if it's a rational discussion. If this is an emotional discussion based on Gino wanting to be right no matter what or you wanting to be right no matter what or Ashby wanting to be right no matter what or even me wanting to be right no matter what, then let's dispense with all discussion of facts, empirical data (the Ashby chart), Principles and application of physics and just take our toys and all go home.

I think we should all be capable of discussing this rationally, though. And here's how that sort of thing works. You provide an argument. If the argument is compelling, I accept it. If it's not, it gets refuted. It's not personal. That's how rational people use debate to arrive at the truth. That's the real purpose of debate - to arrive at the truth through reasoned argument. And that works very well as long as everyone participating cares more about WHAT is right than WHO is right.

Think about this - a 2000 pound sports car traveling at 70.72 MPH has the same KE as a 4000 pound pickup at 50 MPH.

Multiplying weight times speed (And I'm not bothering to convert MPH into fps) gives 141440 for the sports car and 200000 for the truck. Same KE but the truck is packing a lot more momentum. Which is going to be harder to brake to a stop?

Dana, good question. Slam on the brakes on both and see which one stops the fastest and in the shortest distance. Are we to speculate or have we run a test to determine the actual winner in the "which can stop quickest" contest as above?

Another interesting way to look at it is to think about which would do the most damage to your car if it hit you? The 4000 pickup at 50 mph or the 2000 pound sports car at 70.72 mph. That one is hard to tell because the sports cars are built so light that they waste a whole lot of their energy damaging themselves in a collision (while broadhead tipped arrows are designed to NOT waste energy on their own destruction when impacting) but it's another exercise in thought that's interesting.

And they would be surprisingly close, I'd wager, even though we're talking about doubling the weight in this equation, whereas we are usually speaking in terms of 450 grains vs. 550 grains rather than 500 grains vs. 1000 grains (in line with the hypothetical example cited above).

Yet another way to look at it, Dana is this. How hard is it to stop your car at 25 mph? How hard at 50 mph? Twice as hard or 4 times as hard? Let's not guess on this hypothetical since it's actually been tested.

Here's the chart on that: http://www.csgnetwork.com/stopdistinfo.html

Note the braking decelleration distance column. That's the actual distance it requires to brake. 30 feet at 25 mph and 119 feet at 50 mph. That's 4X more for 2X the velocity. That is exactly in line with the physics formula of KE. 2X velocity = 4x KE, so it's not surprising that it takes 4x the distance to stop. That gives us another perspective on your first hypothetical. Distance to stopping is highly dependent upon KE and "distance to stop" is exactly what penetration is when discussing arrow impact.

One of the major flaws in the heavy-arrow-is-always-better theory is that doubling the velocity also quadruples the resistance (stops faster). We see above this is NOT true. That is where the drag formula, misapplied to a medium that is NOT fluid has generated grossly erroneous assumptions.

Papa Bull: "Rollin, you ever wonder how much damage a .25ACP pocket pistol could actually do if it shot razor sharp broadheads instead of flat tipped lead balls?"

Good point! Now if I can just stuff those big, sharp broadheads into those little-bitty cases. ;)

KODIAK: "Something that is 70% water is not a solid, no way you can make that argument which what you seem to be saying. Lungs, skin, flesh, blood ect are all at least semi-fluid to varying degrees, so I believe Shapeshifters argument has some validity. A block of wood is a solid. A lung is not a solid, you can squish it between your fingers. That indicates some degree of fluidity."

Kodiak,

Tissue, soap, ballistic gelatin, and other similar solids are often refered to as "soft solids" to denote the fluid-like traits you mentioned.

PB, what do you mean by your statement, “the force of drag is not operative”, is there no drag on an arrow as it passes through an animal?

Rollin, good point. Soft solids is an accurate description for lung tissue and meat because they aren't hard or brittle, of course, but neither are they fluid or even really fluid-like. They are, indeed, solid, but soft. So the force of drag, which only applies to objects moving through fluid, is not operable. Therefore, we can't use water, air or plasmas as a model for penetration.

"PB, what do you mean by your statement, “the force of drag is not operative”, is there no drag on an arrow as it passes through an animal?"

I mean "there is no drag on an arrow as it passes through an animal". You nailed it. An animal is NOT fluid and drag ONLY applies to objects moving through fluid.

Drag Equation: http://en.wikipedia.org/wiki/Drag_equation

Definition of fluid: http://en.wikipedia.org/wiki/Fluid

If you don't like Wikipedia, google up some other information. It all says the exact same thing. Unless an object is moving through fluid there is no drag.

I assume then, it must be considered resistance? How is that measured in relation to KE and or MO overcoming resistance? I’m no scientist but if I remember right the more MO an object has the more it is able to overcome resistance, or am I off in saying that?

Well, since we're using Wikipedia for reference:

"Friction is the force of two surfaces in contact. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or heat. Friction between solid objects is often referred to as Dry Friction and frictional forces between two fluids (gases or liquids) as Fluid Friction."

"The coefficient of friction (also known as the frictional coefficient) is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials used – for example, ice on steel has a low coefficient of friction (the two materials slide past each other easily), while rubber on pavement has a high coefficient of friction (the materials do not slide past each other easily). Coefficients of friction range from near zero to greater than one - under good conditions, a tire on concrete may have a coefficient of friction of 1.7."

Sounds good to me, but what is a better indicator for overcoming friction, KE, or MO?

This all is so simple to prove, if you have the right equipment. Get an air compressor with variable pressure to launch the projectiles through a chronograph (projectiles will be of equal dimension, only varying in mass).

Launch into clay or ballistics gel at a controlled speed. Make the two projectiles widely different in mass, then adjust the velocity of each so that their KE is equal, but momentum is different.

If KE is the best indicator of penetration, then the penetration of both should be roughly equal.

Do the same thing, but this time make the momentum equal, and the KE widely different. If Momentum is the better indicator, then penetration should be roughly equal.

If neither test results in "roughly equal" penetration, or if both tests show equal penetration, then a different formula using Mass and Velocity needs to be derived.

Where are Mythbusters when you need them?

Kinetic Energy is a scalar meaning that there is no specific direction only a magnitude. Momentum is a vector which means it does have a definite direction and magnitude.

I believe KE is a more static measurement of energy whereas momentum is the more appropriate measurement regarding two objects colliding. Apologize if this has been stated before in one of the previous bazillion replies.

Although I'm not a scientist, I did sleep at a Holiday Inn Express last night:)

I have a question will a bow shoot a very light arrow, say 4 grains per draw weight faster then a medium weight arrow, say 7 grains per draw weight? Is there a point on the light side where the arrow is not absorbing enough energy from the bow to get the most speed from that bow?

Second and a related question, will a heavier arrow shot from the same bow, presumably at a slower speed, travel farther then a lighter weight arrow?

I think the answer to both questions is yes. But it all depends on the specific weight bows, arrows etc.

Potential energy stored in the bow when you draw it back. It is transferred to the arrow (now kinetic energy)when you release the string. Only a percentage is absorbed by the arrow. The rest of the energy is wasted in the form of heat, sound and other things that we generally don't want when shooting a bow.

I imagine, once you get below a certain arrow weight, too little of the bows stored energy is being absorbed by the arrow and too much is being transferred into sound/heat in the form of bow and archer vibration. I think this is why many bowyers disapprove shooting anything much below about 7 or 8 grains per pound because it puts undue where on the bow, makes for a very loud bow with excessive hand shock.

Same answer goes for the arrow distance question. There is a point where the weight of the arrow is too light, but the reasons for lack of distance are complicated. A super light arrow would likely also not be matched in spine very well and so its flight charactersitics would be poor. I guess if you had a titanium arrow that weighed 100 grains with enough spine to handle 50# of energy properly, it may travel well despite the poor performance (vibration) of the bow.

Free Range, I think if you go light enough in arrow weight the arrow won't go very far because the limbs will break due to dry fire. 4 grains per pound might get you there and might not. I won't be trying it on any bow I've got thought, LOL.

As for the 2nd question, Free Range.... it will depend on what your drag coefficient is. Drag is, in fact, at work through air. And you can flu-flu a light arrow and it won't go as far as a heavier arrow despite better initial speed.

Ham Biscuit, the notion that momentum must be more useful in determining penetration because it is "directional" is another misunderstanding. The fact that it is directional does not mean that it is most appropriately used to tell how much energy something has going one direction. KE in an arrow is all going the same direction, too.

The reason Momentum is considered directional is because momentum is only useful in determing some aspects of collision reaction between moving bodies and is only useful directionally. Kinetic energy, on the other hand, is scalar and can tell us a lot simply by knowing the magnitude. Momentum will tell us what direction the arrow is going and whether it will bounce off or penetrate but how FAR it will penetrate is determined by the work being done and the KE available to do the work.

Truck vs. Meatball. http://www.batesville.k12.in.us/physics/PHYNET/Mechanics/Energy/KENOTMomentum.html

What is work? http://www.batesville.k12.in.us/physics/PHYNET/Mechanics/Energy/what_is_work.htm

Ke is used to do work and cutting through a deer is work.

PB, please show some respect, it is an honest question, but if you need it spelled out, try this. 1) assume the bow does not / will not break, and 2) assume the arrows are the same except for the weight, same dia, same length, same head, same fletching, same bow, same draw length, the only diff is the weight.

I’m asking these questions because I would like to know, if there is no reason for 8-10 grains per draw weight, then I can see advantages for going lighter, but I don’t want to go light if I feel I will be losing penetration. Back home in KS it was not that big of a deal, here in CO, where Elk is my main focus I need to feel confident in my set up.

Free Range, I'm sorry if you thought I was trying to disrespect you. That really wasn't the case at all. I was trying to inject a slight bit of levity into the discussion. I actually gave you the honest answer. As long as you adjust the drag coefficient accordingly so you don't turn the arrow into a flu-flu (go light enough and even very small vanes might be too much) and provided the bow can launch the arrow without breaking, the faster arrow will always be the lightest arrow and I think it would take some extroardinary measures to arrive at a combination that would have the heavier arrow travelling farther.

Using the same fletching is not keeping everything else equal. A 300 grain arrow requires much less drag to keep it in line than a 700 grain arrow and, as a result, the 5.5" high banana fletches that work great on the 700 grain maple shaft turn the 300 grain shaft into a flu-flu. The 300 grain shaft would be much more appropriately set up with 3.5" feathers. For 400 grain shafts, I use 4" low-profile feathers for my broadheads. If I went up to 550 grain shafts, I'd probably go to either 4.5 or 5" feathers for broadhead correction.

The biggest problem with the 8-10 grain per pound recommendations, in my opinion, is that they're a poor rule of thumb. A 450 grain arrow from a 45 pound bow is 10 grains per pound (on the heavy side of that formula) and would, indeed, do a very good job on both deer and elk. I go up in draw weight (55#) but keep that arrow weight the same. It generates much more velocity, which generates more speed AND more momentum. It flattens the arrow flight and minimizes high low misses and even though it's under the 8 grain per pound recommendation, it's even more potent from the 55 pound bow than the 45 pound bow (where the "rule of thumb") would actually fit.

There are two ways to flatten trajectory. Go up in bow weight or go down in arrow weight. Going down in arrow weight wouldn't be my choice if I was moving up to bigger game. I would go up in bow weight instead. Arriving at an arrow weight you feel comfortable with and a velocity you are comfortable with, then all that remains is shooting a bow with the horsepower to get that arrow weight up to that velocity. I've had such good results with 55 pounds and 420 grains that I'm probably going to go down to 50 pounds and 400 grains for whitetails next year.

PB,

Chart 4 only covered 39 of the 364 studied kills. It is an FOC chart because those specific 39 kills had varying %FOC and were part of his study on the effect of FOC and FOC only as a factor. Dr. Ashby had numerous charts for visual reference to all parts of his study to include an analysis of both ke and momentum as predictors of outcome penetration which included ALL 364 kills. The empirical data does not show (not even remotely close) what you claim. You're holding up an apple and claiming it to be an orange.

Dr. Ashby not only had personal experience that did not match the current wisdom which is based on mathematical lab theory, but he set out and spent years collecting data from the field to prove or disprove the lab theory. The emperical evidence of this is overwhelming and clear. How you can review the report which clearly states one thing, then you purport something completely different on this thread is beyond me. Even in the Martin test, the slower/heavier arrow penetrated deeper into the high density foam backstop than did the lighter/faster arrow. Again, you're holding up an apple and proclaiming it to be an orange.

Your analogy comparing a 45# bow w/ a 10gr/# arrow against a 55# bow w/ a 8.18gr/# arrow is incredibly askew. Both are pretty much within the rule of thumb making it of little value plus you're comparing two different bows which is of no value. This discussion is reference how ke relates to outcome penetration. Hence, does a lighter and faster arrow outpenetrate the heavier and slower arrow from the same bow? Finally, you say you're so happy w/ your 55# bow w/ a 7.73gr/# arrow that your're going down to a 50# bow w/ a 8gr/# arrow? This is double speak. You've gone from describing the sky as the ground to speaking from both sides of the fence at the same time. I think you have lost your apple and are now calling a banana an orange.

This is not worth the effort and I will no longer offer as I feel you no longer appreciate.

To everyone else with any amount of interest left in this thread, take all this lab coat theory and internet Wikipedia rehash with a grain of salt. Push yourself away from the computer and actually get out into the field to hunt game animals. It will not take long before you begin to develop your own opinions on this topic.

Remember to take a kid hunting, Daddy Bear

Well, yes.... I've been hunting for quite some time with arrows between 400-500 gr. out of bows between 40-50 lbs in various setups. My field experience has shown me that I have no need to shoot a heavier arrow when killing white-tailed deer. Not sure what everyone is trying to say here.... just that I personally know from my experience in the field (no lab coat, no calculators), that my setups get the job done with 400-500 gr. arrows, regardless of GPP, KE, or Momentum. Simple as that, and I surely don't need a report or a ballistic table to tell me that what I've been shooting for over 20 years is not capable of killing deer on a regular basis.

Everyone,

I quickly typed and hit the send button w/out proof reading my last post. I just read it and feel my tone was a bit harsh.

My 8yr old daughter and I are making an instructional archery video for her troop. Yesterday she was shooting extremely well and the video to that point was turning out well. My mother-in-law is here on a stay and to make it short, she is retired ATF admin out of DC and is the self-appointed standard bearer for PETA and Handguns, Inc. My daughter was excited about the video and wanted to show it to the family which was all mom-in-law needed to start on an attack. She did her best to psychologically wound my daughter and it took me to my limits shielding my daughter from the onslaught.

I went straight from that to typing my response to PB which I should not have done.

later, Daddy Bear

Daddy Bear, you think I'm taking things out of cotext and that's your prerogative. Those 39 kills on that chart weren't "hand picked" for their FOC interest, but were compiled from Asiatic Buffalo kills. They weren't cherry picked at all just for HIGH FOC. Dr. Ashby said the restults were suprising and he could only attribute it to high FOC on the lighter arrows.

He was wrong on that, though. He could have attributed the results to the fact that KE is a very significant factor in penetration.

I don't care if you are absolutely positive that Momentum is everything, Daddy Bear. I'm not interested in changing the minds of any one who has convinced themself they have the final answer; one that they've locked up never to be questioned again. I have no problem with anyone believing whatever they want to believe.

I think anyone who hasn't made up their mind yet and is still interested deserves an overall rational view of this, so I try to help round out that view when I can. There's no need to fear that 10 or more grains per pound is necessary lest the arrows bounce right off.

Lighter and flatter is more forgiving and likely to hit the kill zone. Heavier, theoretically "fixes" bad shots. An ounce of prevention is worth a pound of cure, in my opinoin. Particularly if the pound of cure is a questionable cure, anyway.

Daddy Bear I think you need to test your MO theory on your Mother-in-Law :o)

Pappa Bear here is another question for you. If the light weight arrow given that everything else is the same except speed, then why would the same amount of drag from the fletching slow down the lighter arrow faster, causing it to act like a Flu-Flu.

Here’s my thought, it’s because the heavier arrow has more MO, which allows it to overcome the drag more readily. What are your thoughts?

Free Range, reversing the question should reveal the answer for you. If a 3" fletch provides perfect correction for a 300 grain arrow, does that mean it should work just as effectively for a 600 grain arrow?

The answer, of course is: no.

It's like assuming the same size parachute that is ideal for a 50# cargo crate would be ideal for a 300 pound man.

The issue is the drag coefficient. You need to keep them in line to keep performance in all aspects in line. The drag coefficient is dependent up on surface area, mass and velocity and tells us how much resistance drag will give an object moving through a fluid environment.

Drag Coefficient: http://www.grc.nasa.gov/WWW/K-12/airplane/dragco.html (I went with the NASA link since rehashed Wikipedia nonsense isn't deemed valuable by everyone in this thread).

Your thought that the arrow has more MO, which allows it to overcome the drag more readily isn't entirely off base. The real crux of the matter is that the higher the MO for a given amount of KE, the lower the mass and higher the velocity will be for a given projectile. The higher velocity actually increases the drag force, so the answer is to change the drag coefficient by reducing the intentionally supplied drag of the fletching.

To make the point... if your thought was factual on face value, my 512 grain cedars with 5-1/2 inch banana fletches would outperform my 4" fletched 420 grain hunting arrows. The lighter arrows are actually more efficient and lose less energy downrange despite having lower momentum figures. You can't cut the drag coefficient out of the equation and still have a meaningful equation.

Sounds like to me the only way satisfy this debate would be for someone to do a test. Bare shaft shot into some kind of consistent medium, like ballistic jell, first with two arrows with the same KE but different MO, then with two arrows with the same MO but different KE. Of course everything else needs to stay the same, same dia arrow and same head, etc.

I agree that such a test would be good. I think it should, as someone mentioned earlier in this thread, be done with a pneumatic powered device designed simply to shoot rods, eliminating the flex, fletching, release inconsistencies, tuning, etc., and just dealing with the difference in penetration of different weight projectiles being propelled with the same force.

I'm going to check the shed for a pneumatic powered devise, non flex rods, and a consistent medium like ballistic jell.

Let you know how it turns out.

Can I be a Dr. then too?

:^)

Steve

Let me know if you've got that stuff laying around handy, Dr. Steve. :)

Just a quick comparison that I think you'll find valuable in seeing there is an important difference between momentum and KE.

Borrowing some arrow speed and weight data from PeteWard.com (hope Pete doesn't mind !) where he reviewed a Border Griffon Lonbow recently.

Using his numbers, he drew the Griffon to 28" and 49#, then shot with the following results:

412 gr. - 197fps 668 gr. - 171fps

If you calculate both KE and momentum, you'll derive the following numbers for these two shots from the same bow:

412/197 = 35KE - 11MO 668/171 = 43KE - 16MO

That is a 23% increase in KE which is significant but a 45% increase in MO which is basically double the increase seen in KE. Now we just need someone to actually measure the ft. lbs. of energy received by a target when these two arrows hit to possibly shed some light on any relationship between KE and MO.

Also, I'd like to amend the last statement about ft. lbs being received by the target. This is a technically incorrect statement. In a collision, Momentum is conserved between the two objects involved. So whatever force is felt by object 1 is felt equal and opposite by object 2. In the case of arrow and target, most of our targets (hay bale, deer, foam block) have much more mass than our arrow. So basically, the momentum carried by the arrow to the target is also felt back on the arrow by the target. Correct me if I'm wrong here, but that means, while the arrow is penetrating the target, the equal/opposite reaction by the much larger mass target is impaling itself on the arrow.

I think this is why momentum is such an important factor in archery. KE is the measurement of energy available to do work. Momentum is the measurement of actual work done. Work done to move an object, penetrate an object, lift an object. So while it is always a good idea to encourage archers and gun hunters to understand what the KE of their given projectile is (because it is an indicator of the force that projectile could deliver) I would have to opine that momentum is a SLIGHTLY more accurate measurement of the effect an arrow would have on another object.

All that said, I think it is almost futile to try and consider penetration at this level. KE and Momentum both show pretty consistently the advantage of a somewhat heavier arrow. As long as we're talking about the relatively thin-skinned deer, I would think most any hunter would want the heaviest arrow they could shoot accurately at the maximum distance they are comfortable shooting. Both KE and Momentum measurements bear this out. So, If you think you're a good enough archer to make a 50 yard shot but need a 7 gpp arrow to make that shot consistently, then by all means, shoot a 7GPP arrow. If you're shooting elk and Moose, then I think common sense dictates that until a recurve can safely and quietly shoot a 7gpp arrow at about 240 fps, you are going to be dangerously light for those animals.

Ham Biscuit, thanks for posting what I have been thinking about all along while following this thread; namely, that for a given bow, the heavier the arrow you use, the more energy you extract from the bow. What this means to me is that supposing I am shooting a bow that is perhaps considered marginal in draw weight for a given animal. Why would I deliberately handicap myself by leaving "energy on the table" so to speak by shooting a light arrow, when I know that a heavier arrow will develop more of the potential energy available from the bow. Even if all you are concerned with is KE, disregarding all the arguments pro and con for KE vs Momentum, it is still obvious from the above posted numbers that the heavier arrow develops more KE (from that given bow) than does a light arrow. If the bow you are shooting is well above the marginal category in draw weight then I don't see that the heavier arrow has as much advantage. However, I personally prefer to set my bow up for the biggest animal I may encounter (elk) so that I don't have more than one trajectory to learn. My 650 grain arrows(at 160 fps) are fine out to 35 yards or so for ground squirrels on up to elk. I don't figure on shooting farther than that.

Ham bone, I think it would be important to take another review of what momentum really tells us because hmomentum is not the measurement of work actually done. That assumption will cause very serious errors in understanding what happens with ke and momentum at and after impact.

Momentum is, as you said, a vector descriptor and it is always conserved. What momentum tells us is how much the object being struck is going to be moved by the object striking it. The more momentum in the projectile, the more will be transferred to the target in an elastic collision. This transferred momentum is still a vector and it only tells us how much the target will move and how much it's velocity will change.

Ideally, we want the least amount of momentum transferred as possible. Instead, we want to expend all the KE. We don't want to waste energy pushing the animal. We want to cut THROUGH it.

Momentum tells us how much our arrow will thump and push the animal and KE tells us how much capacity for deformation(work) the arrow can provide and it's the latter that we really want to measure.

Greg, you make a good point about leaving energy on the table. Up to a point of diminishing returns, increased arrow weight means increased bow efficiency. However, going down 100 or even more grains in arrow weight from say 600 to 500 grains nets a difference of only low single digit percentage differences in KE, usually less than 5%. Now the important question... why leave that on the table?

For me, it's a matter of sacrificing a small amount of the potential KE in order to achieve a flatter, faster, more forgiving arrow flight. The more you shoot at unmarked distances, particularly competitively, the more you realize just how important speed becomes.

Fishing arrows would maximize potential KE from your bow more than a 600 grain arrow would, so why not use one? Because they have a very slow velocity and that really hinders your ability to place the shots.

You can increase velocity by going down in arrow weight or up in bow weight or even both. If you can shoot a 500 grain arrow pretty well at 50 pounds and are really all that concerned about penetration, you can go up 5# in bow weight and drop 100 grains in arrow weight and still end up with more KE than the 50# setup and a much, much faster, flatter shooting arrow.

Every time you hear about "missed just under" or "missed just over" in the woods, you hear about my reasons why heavier arrows aren't necessarily better and can, in fact, be much, much worse than something flying flatter with acceptable Kinetic Energy.

Ounce of prevention to help keep you from missing - or pound of cure, hoping that when you miss the heavy arrow will bail you out... that's the choice and neither is right or wrong. Your game. You play the hand as you think will work best for you. I only advocate thinking about how to play the odds for your favor and understanding that ligher/faster or heavier/slower is an important decision and it's on a sliding scale with extremes either way being bad ideas. It's a line that starts from way left and tracks way right and you pick a spot somewhere in there with which you are comfortable.

Found everything but the gel - then saw the 200 beefers in the pasture behind my house. Maybe after dark, I'll start my own "scientific" study. :^)

Dr Steve

From Papa Bull: Momentum tells us how much our arrow will thump and push the animal and KE tells us how much capacity for deformation(work) the arrow can provide and it's the latter that we really want to measure.

The trouble with that statement, accurate as it is (and it is) lies in the previously discussed principle that KE is non-directional unless made so. The work the energy does might or might not be pushing an arrow into an animal. It might, for instance, become hydrostatic wave form on impact. It might be expended in vibration at the tail of the shaft on impact, etc...

Since we design hunting arrows to to do sufficient physiological damage, with the least resistance possible (at least I do) we throw a wrench in this statement as well. "The more momentum in the projectile, the more will be transferred to the target in an elastic collision." Though true, as you said earlier, Papa, we are trying to raise momentum and KE, but transfer as little of it as possible to the target animal. Aerodynamics come into play. This doesn't negate what you are saying, but it does add certain dimensions to our discussion.

Regardless, momentum is not only a measure of how much an object in motion will move the object it strikes, but also how much time and resistance it takes to stop it.

The argument concerns penetration, so accuracy is best saved for a different discussion.

It is a mistake to try this test in a homogenous material like ballistics gel. I would vote for a two or even three density heterogenous material and a larger sample.

I am still waiting for someone to help me understand why deceleration at impact doesn't seem to come into play.

If I lose half my speed on an arrow, I have lost 3/4 of it's KE.

If I lose half my mass I have lost 1/2 my energy.

If I gained my KE primarily from speed in the first place, don't I lose a larger percentage of my energy per each lost foot per second?

Too dark to see the beefers to give it a try so I could give you an answer.

Back to the shed to check the supply of 2 or 3 density heterogenous material.

Doc

The reason accuracy comes into play and is pertinent is that it's the primary reason for this discussion, in the first place. If accuracy wasn't important, then steel rebar might be the best arrow shaft material. And there would be no argument to say it wasn't. I mean... if accuracy isn't part of the issue, then who cares how hard it is to get it to the target? But accuracy is an issue and for accuracy, flatter is better.

The reason momentum is considered a vector quantity is because without knowing which direction it's going, it's an absolutely useless value and, in fact, cannot be fully described.

This following statement is not correct "Regardless, momentum is not only a measure of how much an object in motion will move the object it strikes, but also how much time and resistance it takes to stop it."

That's not what momentum really tells us. Momentum tells us about how the objects will respond to the collision. Will they bounce off or will one be absorbed by the other? In either case, momentum is conserved and tells us about which objects will end up with what momentum after the collision. KE tells us how much work (displacement, deformation, etc.) can be done.

While KE can be completely described without a direction simply in terms of it's magnitude, when we're shooting an arrow, we DO give it direction. The KE can, in fact, be used on hydrostatic shock, vibration, etc. and, thus be depleted. And that is why an arrow no matter how heavy it is will not penetrate well if it is a blunt or if the arrow is noodling from side to side at impact. If we maintained a simplistic approach that "momentum tells us how hard the arrow is to stop and, therefore, tells us how well it will penetrate", then regardless of the arrow's vibration, noodling or geometry, it would penetrate exactly the same. We know that's not the case. And the reason that's not the case is because the KE does the work of "penetrating" by mechanical means.

You don't gain energy primarily from KE. The energy of the arrow is made up entirely of it's KE (hence the term "kinetic ENERGY"). No motion, no kinetic energy (also no momentum).

Deceleration at impact really has no bearing on how much penetration we can get because it's the amount of KE that tells us how much work will be done. Penetration is the work we want done. Decelleration is the result of KE expended doing that work, so the decelleration in an arrow at impact is due to the work that HAS been done. By the time we have the decelleration, the work that caused that decelleration is already done, so we can't argue that it's not available to do the work. Assuming that penetration is reduced because of decelleration from the point of impact on is akin to assuming that the tail wags the dog; we've misunderstood the causal relationship.

If I may, I'd like to toss out a few thoughts:

Momentum was originally an attempt by a guy named Jean Buridan at about the year 1330 to explain why iron balls flew farther than wooden balls when thrown at the same speed. Later Galileo called this "momento", hence the name.

Rene Descartes (who taught his students math by playing cards with them!) called momentum the "quantity of motion". Sir Isaac Newton defined momentum as the mass times the velocity.

And now you know...the rest of the story. :)

Quantity of motion is precisely what momentum represents. The energy of that motion is what KE represents. Momentum tells us whether our dollar is in 100 pennies, 2 quarters and 5 dimes or 2 fifty-cent pieces. KE is the value of the dollar, itself, and the actual purchasing power of that dollar regardless of how we arrived at that dollar.

I have to note, though, that Jean Buridan's steel ball vs. wood ball phenomenon, although well explained in subsequent centuries is still with us, mutated into the golf ball vs. ping pong ball phenomenon. Of course we understand now that the physics of movement is too complex to explain, predict or understand with one simple "force" such as Buridan's "momenta".

I love these discussions, although none of that will do you any good in a brick fight 8^).

Accuracy is mostly a product of form; speed can enhance accuracy or it can deter from it, depending on how it affects form...there's always a happy medium and it's different from archer to archer.

Getting back to the brick fight: When dealing with animals, there are many other values and variables that come into play. Attached is a photo of a buck I took a few years back. The penetration on this buck was to the feathers on the entrance side, and sticking out the other side, by what was left of a 27" cedar arrow.

This bow is an old lemonwood selfbow with clarified calfskin (rawhide) backing. The arrow was around 500 grains...a cedar with 160 grain Howard Hill head...5" hand cut feathers. This is what a well-tuned arrow will do at probably 135 or 140 fps (guessing), when put in the proper spot. Also, the arrow was 11/32 diameter wood so penetration would be less than a slicker arrow surface, or smaller diameter.

For its intended purpose, the arrow and bow performed flawlessly, and recovery was quick. A high-speed, small diameter arrow would not have killed it any more dead than it already was.

It certainly keeps the mind sharp to talk of such details, and that's a good thing. Let's just not lose track of what works, as opposed to what makes good discussion. We don't want people to think they can't kill deer under 200 feet per second.

George, thanks. You're right, we don't want people thinking that you have to shoot 200 fps or more to kill a deer or more and I think it's very important we don't forget that as we discuss these things.

Understanding ballistics is an important part of shooting. I would disagree with someone who said that the fastest arrow your bow can shoot is always best just like I disagree with statements that the heaviest arrow your bow will shoot is always best. Both would work, but neither would likely be ideal. The whole spectrum in between those extremes is available and as we understand the nature of the ballistics better, we're better able to select a setup that best suits our bow and our shooting style and our game and our hunt.

I shoot 420 grain shafts for whitetails from my hunting bow even though it will handle 325 grain shafts. The lighter of the two are simply too noisy and twitchy for me to want to set them up with broadheads and hunt with them even though they would definitely drill a hole right through a deer and keep going and even though they're very, very fast (well over 210 fps).

I really like to maintain at least 190 fps because I know how unforgiving 180 fps or less is at those unmarked distances. If I was using a rangefinder, however, it wouldn't matter. 160 fps would be dandy if you know how your arrow shoots at all the ranges you'll hunt and you know precisely what the distance really is.

PB your analysis is correct and reasonable. However, my point was that the bow I'm shooting is at the low end of the acceptable draw weight for elk and I would rather stack the odds a little more in my favor with the heavier arrow. I don't need real flat trajectory out past 25 yards or so because I would probably not take a shot much beyond that distance. For that my 650 grain arrow at 160 fps is fine, particulary if I shoot that combination all year long and various targets and ranges. By doing so I can memorize the arc of the trajectory as spoken of by Kidwell in his book. Once that trajectory arc is imprinted in your brain it somewhat compensates for a flatter shooting bow. If the largest game I would ever hunt is deer, I would likely drop my arrow weight as you are suggesting. Thanks for your educated analysis on this subject. I don't know that everyone will ever agree totally about the KE vs momentum topic, but it makes a for a good discussion on a rainy day (which it is here). In the end we each have to figure out what works best for us as individuals and go with that.

Good reasoning, Greg. It sounds like you've given a lot of good thought to all the right things and I'll bet an elk is going to be in big trouble if he gets in range for you. :)

"The reason accuracy comes into play and is pertinent is that it's the primary reason for this discussion, in the first place."

Yes, but....

In science we must use operational definitions to define the scope of a discussion or study. In my field we don't talk about "What is the best way to treat NH lymphoma?" We discuss, "Does 5000 cGy delivered over 6 weeks of treatment to a mantle field on male patients over 35 yo with stage 3 NH lymphoma show more positive outcomes than 4200 cGy delivered over 4 weeks to the same class of patients?"

I agree accuracy comes first; disagree that projectile weight has a primary negative effect on accuracy, but that is a different thread, as far as I'm concerned.

"The reason momentum is considered a vector quantity is because without knowing which direction it's going, it's an absolutely useless value and, in fact, cannot be fully described."

That's a rephrase of what I just said. Direction is part of its definition.

This following statement is not correct "Regardless, momentum is not only a measure of how much an object in motion will move the object it strikes, but also how much time and resistance it takes to stop it."

"That's not what momentum really tells us. Momentum tells us about how the objects will respond to the collision." Again, a little different phrasing, but partially agreeing with what I said. In fact you used the analogy of two cars stopping earlier to support a point. Yes, you can bring an object to a stop, and yes the energy will go somewhereand each object will have x or y momentum figures.

Bullets are often designed to transfer their energy to the target. I'm trying to get an arrow to go through WITH AS LITTLE ENERGY TRANSFER AS POSSIBLE. I know that doesn't change the Laws of physics, but it has some bearing on which principles or research we go to for information.

"momentum is conserved" Yes, the energy/momentum goes somewhere. and the calcs tell us about which objects will end up with what momentum after the collision.

"If we maintained a simplistic approach that "momentum tells us how hard the arrow is to stop and, therefore, tells us how well it will penetrate", then regardless of the arrow's vibration, noodling or geometry, it would penetrate exactly the same. We know that's not the case. And the reason that's not the case is because the KE does the work of "penetrating" by mechanical means."

That is not a simplistic approach, it is in fact a narrowed approach used purposely to keep on the subject. You are correct in all the assertions about KE, but saying "all else being equal" gets tiresome.

You don't gain energy primarily from KE. The energy of the arrow is made up entirely of it's KE (hence the term "kinetic ENERGY"). No motion, no kinetic energy (also no momentum)." I know this as well as you do. Semantic quibbling is not helpful to discussion, though I did make a mistake or two in verbage. (If I had a quarter for every time a patient said they were nauseous when they meant nauseated.....) Of course I meant our KE NUMBERS and our momentum NUMBERS. I also meant that if our high KE numbers are dependent or heavily weighted toward the squared velocity portion of the equation, then....

"Deceleration at impact really has no bearing on how much penetration we can get because it's the amount of KE that tells us how much work will be done. Penetration is the work we want done. Decelleration is the result of KE expended doing that work, so the decelleration in an arrow at impact is due to the work that HAS been done. By the time we have the decelleration, the work that caused that decelleration is already done, so we can't argue that it's not available to do the work. Assuming that penetration is reduced because of decelleration from the point of impact on is akin to assuming that the tail wags the dog; we've misunderstood the causal relationship."

This is one of the best pieces of informational writing I've ever seen. Good stuff. To narrow the question: Having deccelerated "x" amount after impact and 1" of penetration, (pulling numbers out of the air) how much KE is left to CARRY ON penetrating. Do the numbers change much when we increase the value of weight in the the equation and decrease the velocity while maintaining the same KE number.

It seems that you are making an assumption that many of us don't understand the principles generally, viz your reply here. "You don't gain energy primarily from KE. The energy of the arrow is made up entirely of it's KE (hence the term "kinetic ENERGY"). No motion, no kinetic energy (also no momentum)."

Well, duh, sorry about the wording error.

Why is it so hard to get an intelligent answer, which has not been picked apart for obscure definitional inequities, to the questions I have posed at least three times so far?

Assuming perfectly rigid projectiles with an identical tip, diameter, distance, point of impact, angle of impact, target material, etc..

With different weights and different velocities, but IDENTICAL kinetic energy measurements...

Having no other variable, and taking nothing into account regarding shot placement, bow efficiency, activity of local anti-hunters, bad press, Acts of God, governmental states of emergency, wind direction, angle of shot, altitude, solar flares, butterfly effect, possible genetic variations in the deer, bad Karma, shifting of the magnetic poles, accuracy, education level or force of will of the tester...

Which of the two will penetrate further, or will they be exactly the same?

and..

If a projectile will gain energy exponentially as its velocity increases, will it also lose energy exponentially as its velocity decreases?

Will a less massive or more massive projectile lose a larger proportion/percentage of its velocity given "x" amount of resistance?

One more BTW...

KE is a measure of mass in motion, the ability to do work....and yet..

X-rays have no mass as far as anybody knows, but they will do work. They are capable of ionizing molecules by impacting electrons which do have both mass and energy. They do this by donating energy to the electron until its KE overcomes the atomic bonding energy and it leaves its orbital shell.

Particulate radiation is thousands of times more powerful than x-rays, since they travel at the same velocity, but have mass. However, their penetrating ability is limited to a few microns because of their mass.

X-rays are much less likely to be attenuated by matter, because they do not have mass. However, as you raise their energy, they become more and more likely to interact with matter. In NUclear Medicine they don't even wear shielding aprons because so few Gamma rays will stop in you and do damage, that your total radiation dose is very low even though your exposure is very high.

Now to the point: The new magic bullet in Radiation Therapy is called a Proton Gun. Protons are smaller (less massive) than Alpha particles, but bigger(more massive)than electrons. They possess an interesting characteristic in that they penetrate a very exact and predictable amount through tissues. Protons move through with almost no attenuation to a depth of about 6.2 cm and suddenly just quit, all within a very short depth range, much unlike all other forms of ionizing radiation. They stop because they deposit all their energy within that range.

Interesting, eh? Wonder if it applies....

Springbuck, sorry if you felt like your questions weren't answered.

Question: "If a projectile will gain energy exponentially as its velocity increases, will it also lose energy exponentially as its velocity decreases?"

Answer: Of course. Yes. Absolutely. It's the very formula for KE. What works forward works in reverse, Unquestionably so, no doubt about it. I don't know how much more positive I can be, but I hope that is clear enough. :)

--------------------------------------- Now to the really interesting question:

Question: Will a less massive or more massive projectile lose a larger proportion/percentage of its velocity given "x" amount of resistance?

Answer: No, The lighter projectile will NOT shed a higher proportion/percentage of it's velocity given X-amount of resistance.

Let's do the math:

arrow (a) weighing 400 grains and striking at 198.48 feet per second for 35 foot pounds of KE will exit with 10 foot pounds of KE, so it will be traveling at 106.09 feet per second for a net loss of 92.48 feet per second.

Arrow (b) weighing 600 grains and striking at 162.06 feet per second frr 35 foot pounds of KE will exit with 10 foot pounds of KE, so it will be traveling at 86.63 feet per second for a net loss of 76.03 feet per second.

92.48 feet per second is a greater number than 86.63 feet per second, but is it proportionally greater? No. It's an identical proportion.

Arrow (b) has 0.8165 the velocity of arrow (a) both before AND after it has used (x=25) KE to overcome the resistance caused by the work that was done.

Oh... looks like I overlooked a question from you, Springbuck. Sorry about that.

Question: "With different weights and different velocities, but IDENTICAL kinetic energy measurements... Having no other variable, and taking nothing into account regarding shot placement, bow efficiency, activity of local anti-hunters, bad press, Acts of God, governmental states of emergency, wind direction, angle of shot, altitude, solar flares, butterfly effect, possible genetic variations in the deer, bad Karma, shifting of the magnetic poles, accuracy, education level or force of will of the tester...

Which of the two will penetrate further, or will they be exactly the same?"

Answer: Well, in this case, since we are taking nothing into account regarding shot placement, bow efficiency, activity of local anti-hunters, bad press, Acts of God, governmental states of emergency, wind direction, angle of shot, altitude, solar flares, butterfly effect, possible genetic variations in the deer, bad Karma, shifting of the magnetic poles, accuracy, education level or force of will of the tester, liquid media instead of solid, excessively soft projectiles that deform on impact, etc...

Yes, penetration will be the same for the same KE.

It will require the same amount of energy to cut the same penetration channel to the same depth.

Ahhhh,..... that's better....

Thanks for playing along, Papa.

When you read about some guy studying the flight of wood and iron balls hundreds of years ago, remember that he was trying to understand the flight of an arrow.

Maybe he was using balls instead of arrows because it was cold outside, and his wife wouldn't let him shoot in the house.

You guys all sound like you are way out of my area of enlightenment, but was'nt Howard Hill who said that if it was possible to knock a telephone pole and shoot it he would do just that?

LOL, Hawkeye.... I don't know if Howard Hill said that or not. It's the first time I've heard that sort of quote. Now, if he did say that, do you think that he must have meant that he would rather shoot telephone poles than arrows? Seems he could have shot telephone poles if he wanted. He was good enough to shoot about anything.

And today, Rolin, there are guys studying the flight of ping pong balls and golf balls and their penetration in snow banks trying to understand the flight of an arrow. Now if we could just get folks today to understand that ping pong balls and golf balls (or wood balls vs. metal balls ) are apples and oranges for these comparisons, it would be a small step for an archer but a giant leap for traditional archery. :)

I took two arrows 2117 @ 501.5 grain and a carbon @ 435.1 grain, both had the same broadhead a piece of 1/2 inch plywood. The results are plain to see. I for one will always go to the heavy side.

wingshooter....only plain to see if the arrows were both flying perfectly when they hit the board.

Good test, Wingshooter!

How many inches long is your broadhead?

Now if I could just hit what I was aiming at...(sigh).

George is right. If the arrows aren't both tuned equally well, the best tuned arrow will outperform the other arrow every time. Plywood needs more than 2 hits to make a good comparison. It's density and grain varies significantly throughout. How about trying a fishing arrow to see how it makes out. If every 70 extra grains increases penetration, then the fishing arrow should leave nothing but a hole where it blew completely through.

I simply used the arrows I have on hand that I shoot. Both arrows fly well. I think anybody can duplicate the same test with the same results. I am not interested in shooting dozens of broadheads into sheets of pylwood I just read all this post and decided to see what would happen. I thought the results were pretty obvious. I know for me the results speak volumes. Besides I would rather shoot aerials:-)

I've done testing in foam with the lighter shafts faring very well against the heavier shafts. The tests done by Martin seem to bear out that any well-tuned arrow out of a given bow will perform about the same in spite of weight differences.

Too bad there was only a 66 grain difference in arrow weight in these tests. If anyone thinks we can get an extra 1/4" of penetration for each 65 grains we increase weight, going up from 501 to 601 should blow the arrow through the plywood and going down to 370 grains would make the arrow penetrate a full 1/4" inch less than what we saw in this picture with the 435 grain shaft.

The reason we're still discussing this is because (1) There has never been a conclusive test that satisfies everyone (2) Fellows in the low weight high velocity camp have no problem getting penetration. (3) Fellows in the high weight low velocity camp have no problem getting penetration. (4) Archers can talk but deer can't.

I thought I would give this a try one fish arrow comin up. You were right if it wasn't for the slide it would have gone right thru

Well that settles it...

Plywood isn't a fluid is it? ;^)

by the way the fish arrow weighs 1731.4 grains might be a little heavy to hunt with unless you get kissin close. These shots were from 10 yards.

Wingshooter..... was that fishing arrow tipped with the same broadhead the other two were? Looks like it was tipped with something other than a broadhead and, believe it or not, that will make a big difference. You can punch a hole in plywood pretty easily with a blunt when a broadhead will into it.

Or at least run the other two into the same plywood with the same head on your fishing arrow to keep it apples and apples.

I know.. details, details. Details make a difference, though.

The fish arrow was reagular fish arrow I will see if I can make an adapter to put one of my glue on's on it and give it a try I'm running out of plywood.

Excellent, Wingshooter. That would give us at least an apples and apples look at things even though it's a small sampling. Thanks. :)

"The reason we're still discussing this is because (1) There has never been a conclusive test that satisfies everyone (2) Fellows in the low weight high velocity camp have no problem getting penetration."

Actually, the only reason I care at all is because of my own experience and watching the experiences of others.

At my work there are seven guys besides me who bowhunt. All but me use high performance compound bows between 60-75 lbs, and carbon arrows, usually with modular 3 blade heads or Montecs, that run between 320 and 420 grains. (I'm guessing a little from past conversations, I haven't taken a poll). Their equipment is pretty much what I see almost everyone carrying out here in the West. All of them tell me their set-ups shoot at least 280 fps. They expect long shots, practice out to long ranges, and take long shots commonly. Every one of them claims the ability to kill deer from 80 yards on down.

In the last 4 years among this group, there have been at least 4 to 5 animals hit and lost every year. (There have been 3 brought to bag in the same amount of time). Only one was lost after a pass though hit in the chest, which nobody could believe wasn't found. One I remember as a ham shot. All the rest I remember were shoulder hits, neck hits, or "I thought I got him right in the vitals, but my arrow only went in 4 inches" hits. Most of the time, they tell me about them or their buddy hitting the shoulder or chest and having the arrow fall out as the buck runs, or break off. One hit an elk, "right on the ball of the humerus quartering on". We all take x-rays for a living so we're pretty good on anatomy.

In the same time I have killed 4 cow elk, and one did not pass through. One went through the chest, out the back and hung up in the branches of a fir tree about 30' up. One hit nothing on entry and stopped after breaking a 1 1/2" chunk out of the offside humerus. One stuck in the backstrap after going through the dense cartilage that makes up spinal disks and chipping a vertebral body. It needed a follow-up shot that broke/cut a rib and a lateral spinal process, going in 12" further. This year I centered the 6th rib, splitting the bone almost perfectly evenly for 8" lengthwise. The head was xstuck 3/8" in the offside shoulderblade. I have also shot one large mule deer with a pass through to the chest, no bone hit. Lastly a large-ish doe shooting steeply uphill, where the shot broke a chunk off the scapula on the off side. My closest shot was 9 yards and my furthest was nearly 30..maybe 27-28, I didn't measure...I have hit and lost one deer that spun away as I shot. I hit him in the shoulderblade, I think, and I found my entire arrow broken in the middle. Classic muscle hit bloodtrail...

NOW! I am not trying to prove anything, and I know that there are probably anecdotes about hundreds of opposite experiences. I'm just trying to make this make sense. There is no way I'm generating more KE than these guys. I'm currently shooting 58 or 9 Lb @ 30" Fox High Sierra, which is a great bow, and 560 to 610 gr arrows with heads. I doubt I'm hitting much more than 180 fps, maybe more like 175.

I prefer two blade heads, but I can't imagine new, out of the box, rugged 3 blade heads being unable to penetrate a deer.

I know close shots matter, but I have seen these guys hit pie plates at 80 yards, and soda cans at 50, over and over. Many of the non-fatal hits are well within 50 yards. I've listened to their descriptions of the deer's reaction and what the hit looks like over and over.

I know there are lots of variables, so my isolated experience means little, but why are these guys having this much trouble putting deer on the ground? It seems like it has to be either the broadheads, the arrow weight, or the hits/distance. They swear their heads are the best made.... They swear the hits looked perfect... So why are their arrows falling out? What makes it so that my set-up routinely smashes through bone, when theirs won't?

The best thing I can come up with is arrow weight. It just seems like somehow light arrows use their energy for some "work" other than penetrating work, like hydrostatic shockwaves at impact or something. I dunno...

So anyway, that is the real reason I discuss it. I don't have a better answer, I'm trying to learn more, and I'm not able to figure it out....

Wingshooter's results show nothing regarding KE vs. Momentum.

When you go up in arrow weight BOTH momentum AND KE go up off the same bow (You will see that if you have a chronograph and run the numbers).

So which makes the penetration more....KE or Momentum?

Still at square one.

Springbuck, the fact that they're taking shots that are so long with arrows so fast tells me that there's no way they can know where the arrows are striking those animals and if they haven't set those arrows up to be extremely aerodynamic, they're going to have problems with long-range shots. If they're shooting anything more than a 4" low profile fletching on those 400 grain arrows, they don't have a whole lot of KE left after 60 yards of flight time.

No matter how experienced you feel someone is, you can't assume they really know where their arrow hit on an unrecovered animals and the faster the bow and longer the range shot, the less reliable that sort of thing is going to be.

I've heard everything from broadheads to arrow weight blamed for unrecovered animals when there's no way to know what really happened since the animal wasn't recvoered. Right around 100% of animals lost are lost due to bad shot placement. But rarely do you hear that given as the reason. So I have to take that stuff with a grain of salt.

springbuck, your observations/experiences mirror mine. My friends dad-in-law is a Mathews Pro Hunter and their hunting partner is Chuck Adams. I've watched him shoot a piece of paper the size of a cigarette pack at 60yards. Their stuff is spot on in tune and blazing fast. My friend prefers the faster/lighter carbons.

My rig most generally outpenetrates his on GlenDale targets. Many variables but the outcome is fairly consistent. I've witnessed two spine shots on deer from a treestand inside 20yards where his arrows were stopped cold. I shot one on the same hunt straight down between the shoulders that cleaved the deer through to the brisket. Again many variables but the same pattern.

This is part and parcel with why I enjoy basic archery tackle as everything about it is challenging and nothing is out of the box cookie cutter. What works well for one may not work well for someone else. But, it's all good!

Daddy Bear

PapaBull, that is really exactly what I was trying to say, and why I went to all the trouble to write it all out. Most of their shots ARE long, but some as I said have been well within ranges I would shoot.

I too would likely blame shot placement for most losses, but since there are so many other unanswered questions I keep all the questions at the back of my mind.

Now, one last comment. We're back to the fluids vs. solids argument in some ways, but if a 400 gr arrow loses that much energy over 60 yards of flight through air, wouldn't it also lose a lot on 2" of flight through flesh? I know the laws governing collision are sort of a different set, but really even in the shoulder there is only a couple inches of meat, 1/8" of bone (in the thinnest part of the scapula) and another 1/2" of muscle to get into the chest.

It really doesn't take much to get one lung, which isn't great, but will probably be fatal. Behind the shoulder, I remember pinching the hide and ribcage as I was butchering a medium sized muledeer, and it was less than an inch total thickness to get the chest cavity. I have personally seen a 200 lb man almost die in my ER from a stab wound to the left chest from a knife less than 3 inches long. It had nicked the heart and not even cut into the muscle really, but had hit a coronary artery and the guy's left ventrical of his heart was getting almost no blood to it's muscle.

The only thing int the front half of a deer that I can think of that would stop almost any arrow is the skinny end of the scapula down by the joint. It is thicker bone and T shaped in cross section. They must be hitting that, the elbow, or the sternum.....

The other possible reasons you give are just as likely to be right, PB. Maybe I am looking at the whole deal, thinking that maybe they should be shooting heavier arrows for multiple reasons, including making them less likely to take those longer shots.

papabull, here is the picture, fish arrow with broad head complete penetrarion. I picked up the wrong arrow for the other two the carbon has a 100 grain insert so the penetration was the same the 2117 - 501 the 4560 - 495 The next test is on a 2 x 12 piece of redwood.

I measured each broadhead from center to tip after I dug them out. The fish arrows tip stuck thru the 2 x 12 just enough to feel it. Penatration was 1 9/16 for the fish arrow the 2117 was 1 5/16 and the 435.1 grain carbon was 1 3/16. Just my results in the back yard. My huntin arrows are 628 grain just in case I run into a dinosour.:-)

1713 grains!!! I knew fishing arrows were over 1000 grains but wasn't sure they went that heavy. Now that's a heavy arrow. :) I hope folks don't start buying them up for deer hunting.

Those results are pretty much what I expected. As an arrow goes up in weight, the KE goes up very moderately. But the momentum goes up at a much quicker rate. If momentum was the key, that fishing arrow with the broadhead should have had over 2X the momentum and, therefore over 2X the penetration if momentum-based penetration calculation was correct.

Instead, we see a maximum range of 30% over a very small scale measure ranging from 1-3/16 to 1-9/16 at a weight variation of 430 grains to 1731 grains.

If this is what we consider a good and valid test, then the results tell us that the KE was a better predictor of penetration than the momentum because the super-heavy 1700 grain arrow should have come in at roughly 20% more KE just because of bow efficiency even though normal variances are well under 10% for 100 or 200 grains. And should have come in at well over 200% more momentum. The penetration increase was 30% (very close to the 20% estimated increase in KE and very far from the estimated 200+ percent increase in momentum).

Or we argue that momentum is still the most important factor and discard the test results as completely invalid because the results didn't support our momentum based penetration theory.

Springbuck, you can't use air or water or any fluid as a model for penetration through any solid material. The dynamics simply aren't the same. Through solid materials a projectile has to separate the material at the molecular level. Drag is an entirely different sort of thing and the drag force is unique to fluid and fluid only. This is highly stressed in physics. No fluid = No drag.

To me, the real problem with long shots at game is four-fold. (1) the longer the shot, the more time the animal has to move, particularly considering the velocity of a stickbow shot arrow. (2) the longer the shot the higher the arc and the more likely it will be to hit something in the path between it and the deer. (3) drag. Long shots give drag a lot of time to suck out energy. (4). The longer the shot, the less room for error you will have in your distance estimation and to make matters worse, the longer it is, the more difficult it is to get exact distance estimation. At 60 yards, I wouldn't trust even a laser rangefinder to be accurate enough to get a 160 fps arrow in the kill zone. If it's got an accuacy of +/- 1/2 yard, it won't be accurate enough at that speed and that distance.

here is a new update by Ashley on the KE vs MO argument. Good test results explanations: http://www.tradgang.com/ashby/2007updatepart1.pdf

Ashby keeps saying that KE is a measure of ALL the arrows energy, to include rotational, vibrational, etc.

If that is true, where is rotational speed in the formula?

If you throw a knuckle ball at 70 mph or a fast ball at 70 mph, the KE is the same....there is no variable to allow for any rotational or vibrational energy in the projectile when using the KE formula!

Kinetic Energy = ½ Mass x Velocity2/225218

See? Mass and velocity are the only variables.

BlindMouse1, I see where you are at but I believe you are misunderstanding the Doc's words. I'm going by memory, but your analogy of the two 70mph balls both having the same ke based on their mass and speed are correct. That ke value is the whole kit and cabootle. What the Doc was pointing out was the mistake some are making to equate that whole kit and cabootle as an energy being all expelled and or used up in a directional fasion at, into and/or thru the glove. It is not, by definition the whole kit and cabootle is being used up in many different directions such as rotational, vibrational, etc. This by itself is a reason ke has no value as a predictor of outcome penetration.

Daddy Bear

Daddy Bear, If your believe that KE is useless because it is being used up in many different directions, we need to analyze that a little bit before accepting that the scalar value, because of that, is useless as a predictor of penetration outcome.

First, by ruling out KE as predictable, you are trying to establish that momentum is. But two arrows with the same momentum but with one tuned poorly will NOT penetrate the same. Is that because that momentum is used in different directions such as rotational, vibrational, etc.?

Regarding KE, just because the energy CAN be used for rotation (as in a flywheel), for vibration, as in the result of smacking a tree with a steel pipe, or for work such as cutting... does that mean that when an arrow penetrates, it expends random unpredictable energy in all those ways? On the contrary, the use if Kinetic Energy for work is very predictable.

There is a severe misapplication of the terms being used when asserting that momentum, because it is a vector, is the only (or even the most) accurate predictor of ability to do work in "one direction". This has been the base argument for the "momentum rules" theory but it doesn't stand up to critical scrutiny.

Saying that because KE can be used in all sorts of ways means that it can't predict the amount of work that can be done is like saying that "because batteries can power toys or computers or lots of other things, the measurement of energy in a battery is useless for determining the length of time it can power a flashlight".

Or it's like saying that just because we know that energy is wasted starting and stopping a car - and road friction - and that the car can go many different directions - an estimation of milage we can get from a gallon of gas is useless.

Blindmouse1, You hit the nail. The common KE formula does not include the other forms of KE. It is only the KE of linear motion. The KE produced by rotation and oscillation would be on top of the linear KE, so the total KE number would be higher. If Ashby is suggesting that they are included in the simple formula, then he doesn't have a complete understanding of what he is saying.

oops, Missed!

Papa Bull,

KE is important and is not useless, it's just not a reliable predictor of outcome penetration or terminal performance if you prefer.

I'd be in your court shooting the lightest arrows I could shoot for the greatest speed with a goal of max ke for hunting arrows if it actually worked in the field, but it doesn't. You may get by but it doesn't work in the long run.

Momentum is not be all to end all on its own but it most certainly is a consistent predictor of outcome penetration where as ke is not. And this "theory" most certainly has stood the test of time in the field on actual outcome penetration or terminal performance on game as well as humans when the bow and arrow was used as an instrument of war.

You cannot use the full energy value of a battery for your flashlight to predict how long it will last when others are burning up and using your battery on other toys and such without your ability to calculate what they've burned up. That's the problem with everything your stating as fact to this point. You're predicting how long your flashlight will burn based on a new battery when in fact it's half dead. You're predicting the range on your car based on its tank size and gas mileage. Lets pretend for argument sake that it is in perfect tune and your tires are true running on a flat smooth road. Problem is your tank is only half full and your gas gauge was stuck on full when you started off.

Again, nothing in the field bears your theory out true. If light and fast gets by, well it gets by. But mass and momentum will trump it in the long run.

Daddy Bear

I forgot to add, I have three sets of arrows I'm shooting out of one of my hunting bows. Fairly heavy 10.5 grains/# I use for most big game, 9.5grains/# I'm using mostly for deer and under 9grains/# for small game. They fly a bit different but all fly well. The heavier arrow consistently penetrates deeper into Glendale targets and 4x4blocks than the lighter does. This has been the case for me for decades shooting and hunting w/ basic archery tackle using many different bow and arrow combinations.

PB, I can see nothing you can write on paper or pull off the internet that will overcome my many experiences, game animals I've taken and personal trials and tribulations I've overcome shooting bows and arrows over decades. It's just not there to back up your math. As I've said before, if everone can push themselves away from the computer and just get out into the field to hunt game animals, everyone will soon develop their own personal position on this issue. If yours suits you that's great, but to quote a great movie:

"Don't piss down my back and tell me it's raining".

Best, Daddy Bear

Actually, Daddy Bear, I don't shoot the lightest arrows I could shoot. 300 grains is about as light as I can go. I shoot 420, which is more than enough and has worked very well for me in the long run.

Look earlier in this thread at the fishing arrow that has 2X the momentum of a 430 grain arrow.... Assuming that momentum value tells us how much penetration we should get, we would have expected 2X the penetration by all logic presented by the "momentum is king" camp. It wasn't even close.

The KE posessed at the point of impact is all the arrow is what does the work. Check any physics reference and you'll see that Kinetic energy and work are directly related. There is no such direct relationship between momentum and work.

Knowing how much KE your arrow has downrange is a simple matter of ballistics. You don't have to guess whether your gas tank is half full or if your battery is 1/4 charged or fully charged. We know those values - or at least we should.

With all the threads every year about "missed high", "missed low", and all the subsequent posts commiserating on those threads, I believe a bowhunter would be wise to think about the ounce of prevention instead of hoping a pound of cure will bail them out.

What really aggravates this is that we are convincing guys on the "light" side at 45 or 50 pounds to go as heavy as possible with their arrows, which means we're convincing people with relatively slow bows to make them as slow as possible. And the results show up every year in these "missed again threads".

8-10 grains per pound was always considered to be a good range of weight until we started reading about cape buffalo and Grizzly heads and assertions that 100% of game lost is due to inadequate penetration. That's complete and utter nonsense.

I think it's time we get realistic about this stuff and quit trying to scare bowhunters into making it extremely difficult to place an arrow properly on the horizontal plane with the "light arrow can't penetrate" bogey man, particularly with thin-skinned easily killed, easily penetrated animals like whitetail deer.

On whiteails, you do your job and virtually any legal arrow you shoot out of a legal hunting bow will do it's job. If you don't do your job, counting on a "heavy arrow" to make it a good kill, anyway, is unrealistically optimistic.

Okay, that's interesting stuff but I consider it a different topic. I'm only speaking of ke = penetration.

As to the flatter flight, or lighter bows:

9-10gr/# gives plenty of speed and is plenty flat out of a bow. My 8yr old daughter is shooting well over 10gr/# out of her little recurve and has no problem sinking arrows into a 3D killzone. She's only eight years old with no knowledge of all this mumbo jumbo math and has no problem whatsoever with a arrow heavier than yours. I don't buy it.

Daddy Bear

And I think 8-10 gpp gives pleny of speed and is plenty flat out of a bow. I'd say it's a little over-the-top to be quibbling about 8 grains per pound or 9 grains per pound as the low recommended range, wouldn't you say? Particularly since 8-10 has been recommended since before either of us was ever shooting.

At any rate, whether you "buy it" or not is your business. I'm not trying to change your mind about what you should shoot. As I've said before, much of this discussion on my part is geared toward helping people who haven't already got it all figured out like you do, Daddy Bear.

I agree with PapaBull about the differences in arrow weight often being too small to matter much. I'd shoot 8 gpp if I had some reason to, without hesitation. Remember, the guys I was talking about are shooting 6 GPP on the upper end.

On the other hand, I will likely insist that if you shoot a light arrow a long way with a marginal broadhead and FOC blah, blah etc.. you are asking for trouble.

So it is one of those variables that I try to eliminate along with the others.

Also, I think that the test immediately above does demonstrate some things pretty well, but I do question whether the target material is an appropriate analog. I'd use layers of wet rawhide or something more like that as well as a hard material.

Thanks, all for a few good rounds...

The truth should not be driven by one's view of what arrow weight is suitable or ethical.

If you look at Wingshooter's results, keeping in mind that there are (3) three things working to stop the arrow: 1) the cut width 2) the surface friction of the flat surface 3) the profile of the head as it transitions to the shaft diameter

there is no reason to expect penetration to be 2X as deep for the fishing arrow.

Given that the width of cut is wider, the surface friction (for the flat area) is almost double and the arrow was driven to the appoximately half the diameter of the ferale; it's penetration is about what momentum would predict.

BTW, I shoot carbons loaded with catagory 5 cable in my 50-60# self bows (10 to 15 yard set up, don't even know what they weigh), about 420- grain out of my 55# browning recurve, and the same 420-grain arrows out of my 60# wheelie bow.

The reason for the heavy arrows in the selfbows is quietness and bow lifetime.

canopy

I was waiting for someone to mention "width of cut", canopy. Nothing is ever as simple as it appears, huh? So you think the .30 percent of additional penetration would be correct given the doubling of the momentum. And you feel that theoretically should support momentum (if that's all right).

So let's assume that the theory "penetration is best predicted by momentum" is correct and give it another hypothetical test.

That fishing arrow had 0.78 momentum and got 1-9/16" penetration. So if the theory is correct, a lighter arrow with the same momentum would get the same penetration since 0.78 momentum = 1-9/16" penetration into this test material.

OK... 500 grain arrow at a velocity of 350 feet per second is .778 momentum. Yep, same momentum but a very large difference in KE.

That 500 grain arrow would outpenetrate the fishing arrow by a huge margin. It wouldn't even be close. That arrow has 136 foot pounds of KE even though it has exactly the same momentum.

Now I think you will have to see the problem with momentum based penetration prediction theories. The problem is that they flat out don't work.

Both the Ashby Chart, itself and this experiment tell us that MO is not very accurate as a predictor - not as accurate as KE, anyway.

Want to further evaluate this particular situation? We doubled the momentum and got slightly more penetration.

What kind of penetration do you think we could get if we doubled the KE instead of the momentum?

That fishing arrow penetrated a full 1-9/16". I did the necessary math and got momentum of 0.78, twice the momentum of the 431 grain arrow.

So let's look at another arrow with THE SAME momentum.

A 500 grain arrow traveling 350 fps would have .778 momentum. Cool. Fishing arrow with .78 and 500 grains at 350 fps for .778.

If you're scratching your head..... the theory that momentum is the best predictor of penetration is simply wrong, broken, fundamentally flawed.... Let's just say BOGUS.

That theory predicts that a 500 grain arrow travelling 350 fps with 138 foot pounds of KE would penetrate to the same depth as a 1730 grain fishing arrow at 102 fps with 39 foot pounds of KE.

We already know the fishing arrow will get 1-9/16" penetration. If momentum is a better predictor of penetration than KE is, the 2nd arrow would penetrate 1-9/16, too. Instead, it would penetrate about three times farther, instead.

You do the math. 500 grains.... 350 fps? Same penetration as your fishing arrow? We know better than that. The momentum theory of penetration prediction does NOT work. It's not even CLOSE to being right.

I guess I missed where he said what the speed of his fishing arrow was.....or are you just guessing the speed for your momentum calculation?

The other thing is: you make the assumption that a 500 gr arrow at 350 fps would outpenetrate by a large margin. I think so too, but that's just it....nobody has actually done a test like that to prove it. Results are not always what you assume they would be. We can not settle the argument based on perceptions or assumptions.

Blindmouse, of course, I'm assuming that the 500 grain arrow going 350 fps would outpenetrate the fishing arrow by a wide margin, but it's a logical assumption since the 430 grain arrow that would have been going an estimated 200 fps for the same 40 foot pounds of KE penetrated only slightly less. 70 grains more and 150 fps more should and would yield a tremendous amount of increased penetration.

Arriving at the speed of the fishing arrow wasn't hard. Assuming a 55# bow, the 430 grain arrow would have been going between 190 and 200 fps and generating close to 40 foot pounds of KE. So I rounded to 40 foot pounds of KE and calculated from there to get the arrow velocity. 102 feet per second is about right.

Frankly, it wouldn't take an "assumption" to prove this. What it would take is Wingshooter enlisting the aid of a friend with the heaviest compound bow he can get his hands on shooting that 430 grain arrow out of it into that same board. 80 pounds would get around 280 fps from a good compound with that 430 grain arrow. Still nto even close to matching the momentum of that fishing arrow from that 55# bow (estimated) but I can guarantee it would penetrate significantly deeper than the fishing arrow. I know that because I've shot 80+ pound compound bows. In fact, I was competing with a 92 pound compound so I know what kind of power something like that packs.

All that is necessary is to prove that arrows of different KE can have very different depths of penetration into the same solid material even though they have the same momentum and the "momentum predicts penetration theory" is disproven. It's just that simple. To determine, whether KE or MO is MOST representative is also disproven with the same test because if the penetration goes up with more ke and down with less ke even though MO remains constant, then we can see that KE works where MO does not.

PB, Not scratching my head, I had some work to do.

Blindmouse, I merely assumed PapaBull was correct in his statement of 2X momentum, but given that the arrows were shot from the same bow, and the bow would be slightly more efficient with a heavier arrow it can be estimated.

Assuming a 163-fps. On the 4560 shaft (not screaming fast, but reasonable); the kinetic energy output by the bow would be 25.7-Slug-(feet/sec.)^2 Given: velocity = (1.05 x 225218*KE of bow x 2 divided by grains of arrow)^0.5 (square root of this quanity)

The speed of the FishArrow approximately equals 83.7-fps were I assumed the bow was 5% more efficient with the heavier arrow. (See Joe Tapley’s pages or Google virtual mass archery).

Where Momentum = Mass (grains)X Velocity(ft/sec.)/225218 = 0.644-Slug-feet/sec. for the FishArrow.

And 0.315-Slug-feet/sec. for the 4560 shaft.

This gives us a 2.04 ratio on the momentum.

PapaBull, I guess we’ll have to agree we disagree.

I must get back to work.

canopy

Canopy, we arrived at the same ratio, so I know we're on the same page there.

Now, let's use your momentum of 0.644 slug-feet/second.

That 430 grain arrow at 325 feet per second would generate momentum of 0.62 slug-feet/second. Somewhat less than the fishing arrow at 83 feet per second.

Wanna bet which one penetrates farther now that we've nearly doubled the velocity of that 430 grain arrow?

The 430 grain arrow at 325 feet per second shouldn't penetrte deeper than the fishing arrow at all if the theory that momentum predicts penetration has any merit. Fact is that 430 grain arrow going that fast would significantly outpenetrate the fishing arrow. DESPITE having the same momentum. Why? Because it has more KE. And because it has more KE, it can penetrate deeper. Momentum has no bearing on it and I think with your logical mind, you should be able to see that, now, using this example, canopy.

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