Help deciphering wierd results from a tuning test with GT Trad's

[fireball31]

Well here is the issue. I have GT Trad's 75/95. I'm shooting a Liberty English. It is 66" long 60 lbs, at 27". I'm pulling to exactly 28". I'm assuming a 3 lb per inch gain which puts me at 63lbs of draw weight. The Strike plate is so narrow as to be inconsequential to the test, Seriously its paper thin. I'm shooting a 16 strand fast flight string.

Test 1. Full length shaft 32" 50grn brass insert. 250 grain field tip.  Bare shafts slightly weak, but close enough to fletch. According to stu's calculator this shaft should have a dynamic spine of 48.1

Test 2.  same arrow, same length, same insert. 145 grn tip. bare shafts slightly weak. almost exactly the same as test 1.  According to the calculator this setup's dynamic spine is 69.3


Did I just get lucky? am I doing something wrong. I would really like to cut these things down in length but the test results have got me thinking otherwise. There is no chance of a "false reading" because of the arrow striking the riser. I would hear it. I'm shooting indoors.

[longbowben]

I think your arrows are way to much spine i shoot 60 plus pounds at 29 and 285gr tip and 3555 full length fly like darts.Just my opinion.

[fireball31]

TTT for the day crew.

[psychmonky]

That arrow sounds WAAAYYYY stiff. I've heard of overly stiff arrows actually showing weak. If that is the case, I would say that your setup is just so stiff that the difference in tip weight just isnt showing up.

Scott

[RM81]

My bows that are around #60 like a 5575.  I draw just under 28" and have about 250grns up front.  I agree with Ben, that 7595 is too stiff even with a bunch of weight up front.  Do you have a full length 5575 or 3555 to try?

[Mint]

When you test arrows that are so way off spine weird things can happen with bare shaft testing. I would see what Stu's calculator comes up with and then get the shaft close to that so you can teak for perfect flight. I think the 75/95 will be overspined for that bow due to not being center shot.

[fireball31]

That's what throws me off. Stu's calculator put me within a pound of dynamic spine with a gt trad 75/95 and 300 grns up front total. with the arrow cut to 29.5.

[JamesKerr]

I agree I would try a 5575 gold tip shaft with a lot of weight up front. Your other option would be a 340 spine carbon shaft loaded up front and left long.

[Greg Skinner]

I would probably try a couple of fletched arrows with big broadheads the same weight as your field points and see how they shoot before cutting or anything else.  Allen cuts his bows closer to center shot than other Hill style bows so it's possible that it could handle that stiff of a shaft, but 75/95 seems pretty stiff regardless. I've used Stu's calculator with good results, but with individual bows it hasn't always been right on.

[JCJ]

I used to shoot a Liberty English that was 56# @ 28" and I drew the bow 30" so it was about 62# at my draw.

I shot Beman ICS 340 shafts full length which is  32". I put a 100 gr. brass insert in and used a 250 grain field tip for a total of 350 gr. on the front.

The arrow shot perfectly through paper and on the range.

Hope this info helps.

[fz4vgq]

Fireball, you might be on the right track. I know every bow shows different results with Stu's calc. I have a boo core Shrew CH that works perfectly with what Stu's calc shows. I had another Shrew CH with the same # specs but with carbon & foam limbs that needed a spine 10#'s heavier than what Stu's showed. But.... most bows I've shot so far do seem to prefer spine weights lower than what one would think.

With your bow, I'm guessing the shelf cut is +1/8" ???  Here is what I get when using Stu's calc for your setup. I have best results with showing the insert as a footing (measure how far the insert goes into the shaft (50gr brass inserts for GT's are approximately 1.0" if I remember correctly).
 

[metsastaja]

Using a 50g insert the weight should be placed in the insert box.  No values should be used in the Footing box since the 50g insert is not longer then a regular insert. If on the other hand you are using a 100g insert the weight goes in the insert weight. Footing is marked Yes and the footing length is set a .50 since a 100 g insert is .50 inches longer then a normal insert.

This information is directly from Stu.

Since Liberty is a modern longbow I would use reflex deflex longbow

The calculator posted above is one of the older ones.  Many changes have been made since.

Here is link to the current version
 http://www.heilakka.com/stumiller/

[fireball31]

actually on the newest version he actually has the Liberty, English