I have stumbled onto a new thought/variable in how we measure draw weight that also explains why we see so many reports that a bow's measured draw weight differs from the bow's markings. I think it worthy of a note and perhaps help thinking this through.

Skipping details, I received a bunch of used Beman ICS Hunter shafted arrows in 400 and 500 and because they had several different (hidden) internal weight and component combinations, with my recuts to two of my bow's preferences, they were not flying right.

With Detective hat on, I eventually found the hidden weight problems and got the arrows correctly spine matched, but before the weights were discovered, one re-check was my bow specs. Instead of my normal process of taking an actual draw weight measurement and using THAT in Stu's Calculator (DSC), I decided to do an actual 28" length weight test, and altered the DSC archer draw length to my draw of 27 1/2" on one bow and 27 1/4" on the other.

The resulting arrows grouped great, but show weak (I'm a Lefty, so the groups were left of aim by 4", often more, at 25 yards.). Why? And why, measuring this way was I getting these weaker than existing shaft specifications? Well some are the variables in consistent draw length, nock tension and such, but those were minor considerations.

What I discovered was that if I put the hook of my scale on the string, and with a test shaft draw the SOP 26 1/4" to the grip throat to get a consistent bow to bow 28" weight/draw length measurement; I get a result of X pounds. BUT BUT BUT, if I take that same test shaft and draw with my finger size, I have to pull back almost another full inch to get to the same 26 1/4" point.

Huh? Because the scale's hook is bearing only on perhaps 1/16th inch of the string, the drawn bow's string angle is more severe than drawing with more than two inches of fingers and glove/tab.

Now, since the DSC can't really know where a bow begins to pile on more pounds per inch of draw (stacking), Stu used an average. But a one inch draw length difference with some stack up involved can EASILY cause the arrows to be too weakly spined.

conclusion/speculation:

If you measure a bow's draw weight by attaching the scale hook and pulling the bow the prescribed 26 1/4" to the grip throat, you will get a result probably LOWER than what the bow actually delivers and likely different than the maker's marking.

It is still better to know what the bow actually draws for YOU by measuring it, but not simply by using the scale hook. You must take a full draw with fingers and glove tab on and have a helper mark a spot on the test shaft in alignment with a spot on the riser. Then you can use the scale/hook to pull the bow to that marked length. This is the only TRUE and accurate way to know what the bow produces with you as archer. Averages might work, and in a long-no-stack bow the difference between you and the lower scale/hook result might not be enough to matter. But especially when that difference in pull distance between fingers and hook involves some stackup of pounds, the difference between you and "average" can make a big change in the best arrow spine and so best accuracy.

Rick

Just put a clothes pin on the shaft, draw the bow, the clothes pint will slide down the shaft and end up at the back of the bow when you reach full draw.Let it down, put the scale on it draw it to the clothes pin. I've been doing that for 30 years or more.

Measure all my bows that whay then I'm tuning them for me.

fdp -

Or you can forget the whole thing and just tune the bow/arrow to whatever weight it is. This negates mentioning that fact that two different bows with the exact same draw weight may, in fact, require considerably different arrows, or two bows with different draw weights liking the same arrows.

Classic overthinking.

A pound or two is rarely going to make any difference in your ability to tune a given rig or shoot for that matter.

Viper out.

Rick - I totally get your thought process there, because that’s the sort of analyze-it-to- death approach that I generally take to, oh.... Just About Everything.

But FWIW....

Einstein supposedly once said that not everything that can be counted actually counts, and that there are some things that cannot be counted that REALLY count.

Or words to that effect. Which is why Stu’s calculator has that “personal form correction factor”.

The calculator will get you close, but it’s up to you to get it dialed, right?

(Alternatively, you can drop the comma and the question mark from that last sentence...)

LOL...

Good point Rick--and like you, I can think of plenty of reasons why someone might want to know exactly what they're drawing--comparing two different bows, for instance.

Your observation could be especially significant when the bow in question is an Evil Dwarf Bow of 56" or less, given to all sorts of nasty tricks like finger-pinching and stacking and spraying arrows all over the range.They must be monitored especially closely!

Good point, Rick. I never thought of that but it makes sense. Jawge

Thanks guys.

Yes the two bows I'm working with are 56" and 52" so the full draw/pinch/stack issues do aggravate my fix-these-Beman's project.

I really like FDP's clothespin idea. Way easier than calling my wife to come mark the shaft while I'm at full draw.

Tony (Viper) says we are overthinking it. Sorry Tony, but not really. You are, as usual, correct that a couple of pounds difference in arrow spine doesn't make much difference as to the ability of a bow to tweak them to best flight. BUT, tweak the bow to one particular arrow spine vs. another that is a little different and the bow will shoot either arrow well, just not to the same place.

I have three bows marked at #55, #47 and #42 that with variations in strike plate distance ALL can shoot the same arrow spine. But after only a short time I abandoned the idea of using the same arrows for all three. Given the power variables they won't shoot to the same trajectory (duh!). My little Browning Cobra at a marked #42 requires a 400 grainish weight arrow to fly to a similar trajectory/sight picture as the #55 bow flings 500 grainers.

So I'm also Un-tuning. Better for me to forget commonality and combine the important (GF is right on here, some details are important, some not so much) of the individual bow's arrow spine and weight, strike plate position and such so they all throw arrows to the same sight view/ elevation.

Rick

Rick -

I love ya bro, but for me the only thing that matters is where the arrows go (and what I have to do to get them there).

Now, I don't have a 28" draw length, and since I'm only using ILF rigs for any serious shooting these days, the bows I'm using will rarely be anywhere near the marked weight.

The "marked" draw weight, like static arrow spine will only get me in the right neighborhood. And yes, I do check the final weight on a digital scale (with a hook), mostly out of curiosity. Since every bow I put on the scale will be weighed the same way, the difference between the hook and my fingers becomes a wash. See where I'm going? To be honest, I thought about the same thing when I got my bow scale, but a little thinking allowed me to understand and dismiss it.

As as I said above, and it bares repeating, the weight of a bow alone only a ballpark indicator of required arrow spine, and that ball park is pretty big.

BTW - I can't speak for everyone's anatomy, but most people do use their middle fingers more than the other two, and the index and ring fingers are "helpers". In a lot of cases the string angle has it's apex around the middle finger - and yes, it's a variable.

So again, technically correct; functionally, not so important.

Viper out.

Viper says,

"Rick - I love ya bro, but for me the only thing that matters is where the arrows go (and what I have to do to get them there)."

Tony, I agree with you and the others who mention that we often get too anal, that some of this stuff matters little.

BUT, But, but...In this circumstance it turned out to be a matter of "they were NOT getting there". A little thing turned out to be significant this time.

In the interest of brevity, I had to leave out background detail and some specifics. Let me try again.

1. Got some used arrows needing re-tunes.

2. I changed from my normal measuring of draw weight for the DSC to another way.

3. The resulting arrows were too weak.

4. Traced it to a difference in draw weight between using the scale hook to draw to full or using fingers BECAUSE my DL hits these bows as they are beginning to add on more poundage at stacking point than the DSC's average pound/length change can allow for.

5. Can't use the DSC's "Personal Form Factor" because the issue was/is bow specific based on stack point(s).

6. Shared all this with my first post. (Poorly I guess)

7. Concluded again that measuring true draw weight beats trusting the DSC's inability to change results properly when the archer's DL is into the bow's stacking range.

8. Advised that this is probably minor with longer draw bows, but not this time on me and my shorties.

9. Concluded that to get an accurate Draw weight entry at least for me and my shorter stack bows, drawing to full with fingers, marking the test shaft and THEN using the scale to draw to that length gave me the proper arrow spine, while trusting the DSC to adjust between a 28" scale only draw weight and my shorter draw didn't work here.

The end

Rick

Rick -

That's cool and I'm not doubting you. It's just that your analysis and reasoning is anecdotal. While a nice to have, and it can be suggestion when things don't add up, it has to be approached with caution.

In the example I mentioned, I have two sets of limbs that are marked AND scale 4# part. Using the same riser, with the same settings, same string, and SAME arrows, the bare shafts react identically.

So, I'll see your anecdote and raise you 4#.

Point is, unless there are very specific circumstances at play, and pretty tight tuning involved, for most people, a pound or two just shouldn't be the first thing to track down. Kinda why AMO suggests that users measure the DL to the back of the riser pivot + 1.75".

Look, we can both get pretty technical on this stuff, the question is, in my mind anyway, should that be the first thing people start looking at?

Viper out.

Who cares what the numbers are. They will drive you more nuts. I big pail of different arrows a ladder and another archer to stand on the ladder behind you. Good arrow flight is more important. Rooty

I just dug out my scale a couple hours ago to get my black super Kodiak ready. To the grip at the prescribed distance it's 52@28. To the back of the bow at 28 it came out 52@28, so both ways work out with the SK. It's marked at 50,well within ammo limits. If 2 lbs either way makes you need new arrow you had the wrong ones to start with. Btw ammo standard is +- 2 lbs of marked weight. Even most custom bowyers use that.

AMO is and always has been voluntary, so even many of the old manufacturers did their own thing. We were taught early on to measure the arrow to the back of the bow, since that is where we need to clear. We added an inch for broadhead clearance and that was that. As long as you do it the same everytime, it doesn't make a hill of beans difference. I'd just as soon watch box turtles procreating. Oh wait, I saw that today.

AArgh,

Should'a kept my fingers off the keyboard.

YES YES YES, any draw weight change of a couple of pounds is inconsequential most of the time. This was an exception which I thought worth sharing.

Something normally not significant WAS this time.

I get it. Under typical circumstances, the draw weight difference measuring with the scale hook on the string and drawn to the SOP 26 1/4" versus drawing with fingers to 26 1/4" isn't enough to matter. Slight draw weight differences are easily mitigated with such tweaks as brace height or strike plate thickness.

This particular bow stacks on enough extra pounds between 27 and 28" that Stu's calc, using the scale to pull to my DL and using my fingers to get to that DL changes the ideal spine arrow by nearly TEN POUNDS.

With tweaks and the difference between a casual draw back and really getting my back into the draw, the ideal spine arrow goes from 53 to #62!

I can get either arrow to group well if my DL/anchor is consistent, but that much spine change alters target impact nearly a foot left/right at my 25 yd. target.

Way too big to dismiss as overthinking this time.

R.

"This particular bow stacks on enough extra pounds between 27 and 28" that Stu's calc, using the scale to pull to my DL and using my fingers to get to that DL changes the ideal spine arrow by nearly TEN POUNDS."

Hey Rick. Now that is confusing, which is probably why I don't bother with interactive charts on dynamic spine. I have yet to not get quality arrow flight by using the weight shown on my Hansen scale, drawn to my draw length with the hook right under the arrow nock, to get my static spine..to work my gozintos. Maybe that isn't exact in real life, but it sure has worked well for me for a very long time.

Hi George,

Can you imagine the Pandora's box of responses I'd get if I mention in too much detail how well Stu's Calculator finds the right arrows for me even though I've been doing it wrong...sort of?

I would typically draw using the scale hook to my nose on the string/chin anchor. I'd enter that draw weight but not change the 28" draw length default. That SHOULD result in arrows on the weaker side of ok, IF I actually drew 28".

But they always came out close to ideal,,,just some minor tweaking.

Why? Because I don't draw all the way to the 28" default, so what'd be weak if I drew 28" becomes spot-on when drawn shorter. One too-light entry mistake is cancelled by one too-stiff error.

R.

Hell, for this bow I ended up just shooting a bunch of spines last night until I found an arrow that flew to center (making sure I got her all the way back), entered those specs. into the calculator to tell me the dynamic spine and then cut the project arrows to that stiffness. Success.

That said, I then ran this high end expensive custom against my old standby Browning Explorer "Baby". Fancy bow at 25 yards delivers softball groups where I am intending. Took out Baby and was busting nocks with 1" groups. Fancy bow got hung up on the rack. Baby went into the truck as the primary hunter.

Rick -

I know there are some who think otherwise, but the last thing I (and I believe most people) want is a bow that stacks anywhere near their draw length. For that matter, once a bow starts stacking pretty much all calculations go out the window.

Relating your findings, even in an isolated case is great, but as was seen on this thread, there are going to be people who buy into it without reading the fine print. That's why I had to stick my .02 in.

The unfortunate thing is that in the trad/internet world in happens more often than not. It's how myths get started and people start worrying about stuff than just don't matter.

Viper out.

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