From: I Hunt Mexico
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Date: 18-Dec-14 |
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I am trying to get some GT 75/95 to fly out of a Treestick. 64# past center shot bow. With the aluminum insert they are spine stiff. with 300gr BH and FP. But I can add 72 gr nut behind the heads and they fly straight. I though that it would be simple to get 100gr brass insert to solve the problem of the arrow spine. But I read last night that the long brass or aluminum insert are like a footing and stiffen the spine. I would like some input before I order the inserts and collars. If it is not going to help.
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From: Pappy 1
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Date: 18-Dec-14 |
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100gr. brass will weaken the spine.As far as I know that is what they are made for to add weight and weaken a stiff arrow. Pappy
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From: yorktown5
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Date: 18-Dec-14 |
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Yes its confusing. Adding weight DOES weaken the overall flex of the shaft, always. Some shaft brands, with more thin walls, do get slightly less weak, not more stiff, with long inserts since that 2" or so behind the tip can't flex.
Adding a 100 grain insert (VS a GT insert weighing 11 grains) to a 7595 shaft weakens the shaft by about 13#. Adding 100 grains to a thinner walled shaft needing an adjustment for the longer insert weakens the shaft by 10.5#. See?
BTW Stu's Calculator says the GT Trads do NOT require adjusting for the longer insert.
R.
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From: George Tsoukalas
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Date: 18-Dec-14 |
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The static or actual spine stays the same. There will be no change on a spine tester.
The dynamic spine is weakened. In other words, the arrow will flex more as Pappy and Yorktown described.
Whether or not that affects arrow flight depends on the bow. Jawge
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From: George D. Stout
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Date: 18-Dec-14 |
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I think very few people really understand dynamic spine nowadays. If you you can't visualize how it works, they you may struggle with getting it done.
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From: I Hunt Mexico
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Date: 18-Dec-14 |
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Per Stu's calculator, I am really screwed up. My bow is at 88# and the 75/95 are at 43# Yet in the real world. I need the extra 100 gr to get the arrows to fly right. BH, FP and bareshaft. I am so confused.
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From: bndhunter
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Date: 18-Dec-14 |
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I could see the 75/95 being 43# if you still plan on using the 300 gr BH. But since you are adding the 100 gr insert you will have to go down in point wait also.
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From: woodsman
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Date: 18-Dec-14 |
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Perhaps people get confused by dynamic spine because they don't shoot arrows to determine what's correct for them.. We rely too much on a computer and some chart. Especially with carbons.
Archery is still a very individual thing and results may vary from person to person.
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From: Zmonster
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Date: 18-Dec-14 |
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I think the 75/95 are WAY too stiff. Even with 300+ up front. Try 55/75 with that much up front and you'll be closer.
I'm shooting a recurve cut past center, 63# at my draw (27") and 29" 15/35s with regular inserts and 125gr heads. Through paper and bare shaft they fly great. I was shooting 55/75 weighted down quite a bit with mediocre results, but accidentaly shot a 15/35 and was amazed. Give it a try, you may be surprised too.
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From: George Tsoukalas
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Date: 18-Dec-14 |
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Yes, indeed, woodsman. Spine is how stiff the arrow shaft is. Period. Putting a heavy weight on the front of the arrow will make it flex more. To cut down on flexing a stiffer spine may (or not-depending on the bow) be needed.
Jawge
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From: M60gunner
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Date: 18-Dec-14 |
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I was reminded the calculator is a starting point yesterday. I used it for a bow- arrow combo I wanted to try. The readings were almost the same for bow and arrow. But when I shot the arrows the flew stiff. I had to go from 145 to 175 grains points to get the correct flight. Lesson learned agian, the proof is in the shooting for me anyway.
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From: I Hunt Mexico
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Date: 18-Dec-14 |
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If I use the 100 gr insert along with the 300gr FP and BH. My arrow will weigh 800 gr. Or should I try a 55/75 and keep my arrow will be about 620gr.
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From: Dan In MI
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Date: 18-Dec-14 |
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One thing I didn't see mentioned. If the 100 gr insert is much long than your AL insert that can change dynamic spine too as you have less shaft flexing.
I also remember some discussion years ago about long inserts that were passing the contact point on the riser (towards the archer) that affected spine. The theroy there was the contact point was the pressure point for the intial bending node and the long insert conflicted with the side plate contact affecting the initial bend.
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From: Orion
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Date: 18-Dec-14 |
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Dan: If you're talking about O.Ls 5-7-inch long inserts, they actually contacted the inside of the arrow wall for most of their length, and that's what made them stiffer. The final 5-7 inches of the shaft just didn't bend. In addition to getting more FOC, the intent was to further strengthen the arrow behind the point/insert where they usually break, if they're going to break at all.
S.S.: Another reason the Axis don't seem to respond as conventionally expected is their narrow diameter. It makes the arrow more centershot, thus requiring a higher static spine out of most bows. Or, put another way, because they're more centershot, they don't (need to) flex as much and can handle more weight on the end without immediately showing the effect.
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From: Backcountry
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Date: 18-Dec-14 |
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Where can the 5-7" long inserts be purchased for GT shafts?
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From: Dan In MI
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Date: 18-Dec-14 |
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I was talking 2-3" but it's the same effect, just not quite as bad.
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From: Orion
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Date: 18-Dec-14 |
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Back country. As far as I know there were never made available for sale. When I think back on it, it may have been Ed Ashby who was experimenting with these long internal foots. Might contact him for more information.
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From: ga bowhunter
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Date: 19-Dec-14 |
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how long are your arrows?if u cut them they are way stiffer than 75/95
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From: Backcountry
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Date: 19-Dec-14 |
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Tuning the GT Heavy Hunters I got from Big Jim might be easier with extra long aluminum inserts. They bare-shafted weaker than expected considering their walk thickness.
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From: I Hunt Mexico
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Date: 19-Dec-14 |
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Concerning my problem. I am shooting them 32.5 inches. If I cut them down they will only get stiffer. I am at a weight that I am finding to be difficult to manage. The way carbon are rated 300 def as the GT 75/95 are to stiff. 55/75 are 400 def, way to weak. AD Hammerheads likes at 375def spine at 72# and they are to weak.AD hammerhead heavy 260 def, spine at 95# way to heavy. 75# POC is to light. Granted I can always build out my strike plate. But I am trying to find another solution. It would be great to finish with a 650gr arrow instead of 790gr. But I guess I will have to live with it.
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From: yorktown5
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Date: 19-Dec-14 |
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Yes, to some very insightful comments about carbon shafts. Just "different", and we haven't or may never get our arms around the physics behind why with complete solutions. Steve's observations are consistent with others, including me, as to what the heck is going on.
To Orion's point, they ain't all alike in construction and so any overall conclusions, other than there aren't any overall conclusions, can be made.
I am a huge fan of Stu's calculator, and along with a few others, had the prototype of the latest version in order to provide him with comments and de-bugging.
Because I have gone through so many bows of my own and performance tuned for others, I've used the DSC a lot. So I write this with confidence: If your results don't work, it wasn't the program. Something is amiss with YOUR inputs. REPEAT:
IF YOUR RESULTS DON'T WORK, YOUR INPUT DATA IS WRONG.
I concede finding where the goof occurs isn't always easy, but trust that it IS there. And the list of possible errors is long. A partial:
-Components don't weigh what you think they do. -Your bow's true draw weight at your draw is seldom what the bow is labeled. -Nock tension and finger release variables alone can make a 5-8% power difference. -Draw length is to determine a long enough arrow, not actual draw weight. Stu can't predict with precision how much real thrust the arrow is receiving as draw weight increases and decreases on a bow design specific basis the further your draw is from the 28" standard. -Stu does a great job of giving the archer choices based on the number of strands using low-stretch string material (but not all the materials are identical). Nor does he allow that dacron strings are commonly found with from 12 to 18 strands, and so will perform differently. -Nor can Stu tell if your string is correctly built and twisted up. -Brace height impacts the results too. -Stu refuses to disparage ANY shaft brand...but if you were to twist his arm and get him to say which brands show best consistency from batch to batch, GT trads won't get mentioned. (Example: I Hunt Mex., the latest 75/95s are 340 spine, older ones were 300s) -Stu's efforts to fix a common input error (strikeplate position) by getting as many measurements of popular bows as possible was a good try. But the presumption that a custom bowyer makes each one identical, or even the production houses delivering bow-to-bow consistency is suspect. Bear for example had as many as 17 bowyers working each of three shifts, and once you handle enough of them, it becomes clear there ARE differences, even between the same bows of the same year. -Carbon shafts want to fly true, flexing only as much as the string really delivers, and can still be more accurate than archer skill even if off-spine by a good bit.
Yes, there is more, but you get the idea. So...
The fixes are: Measure your own true draw weight at your draw length then ignore the adjustment for draw length difference away from the 28" standard. Just use 28".
Ignore a bow specific model, just use generic recurve. (This relates to my testing that when performance setup equally, there isn't enough difference to matter.)
Double check your centershot strikeplate inputs. As little as a 1/32" error changes the results.
Do these things correctly, and the DSC delivers correct answers every time.
Rick
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