Stu's Spine Calc. off by 20#???

[nschlag]

So I have a psa 43 @ 28, drawing around 28 3/4 ish.

I have some trad only 500's that are full length (31.5").
bareshaft tuned and I am grouping just slightly below my fletched arrows.I have even shot through paper and am quite satisfied with the way things look.

When plugging the numbers into the spine calculator i have nearly a 20lb difference in my setup.

What gives? Any ideas.

I am using the standard insert (not sure of weight), 175 gr. points 3 5" fletch with wrap.

Should I just keep flingin n' grinnin or what?

Thanks!

[metsastaja]

what is your center cut and string type. using 3/16 and B50 I came up with less then two lbs.

you might want to read the instructions to see if you are using correctly.

[nschlag]

metsastaja,

i am thinking that my string is a fastflight. not sure how many strand? i just ordered a new string from black widow, i figured a 12 or 14. i was under the impression that the calculator took into consideration what the center cut is, but my widow is -3/16 past center. plus calf hair rest thickness.

[AKCrazyhorse]

did you measure the draw weight or are you just taking the limb markings at face value?  I have yet to see one 20 lbs off but I see them 5-7 lbs off all the time.

[BCWV]

Widows like a stiffer arrow being cut past center and I would think you would be underspined with that arrow setup.
 I used to shoot the same arrows out of center cut bows pulling a little more than yours and had to cut em back to make them stiffer.
 Having said all that, if it working for you I'd shoot em.

[nschlag]

crazyhorse, i don't have a scale so i am limited to assuming bw measured it accurately.
BCWV i tried some 400's that were cut to 29.75 bop but they bareshaft stiff and no amount of weight will fix it.

thanks for the feedback

[xtrema312]

Every widow I have had liked arrows way under spine per the calculator.  Most shot the same arrows I shot in my other bows cut to or just short of center when the bows were all of about the same draw weight.  Bare shaft and paper tuned just fine like you are getting.  Stiffer arrows didn’t seem to work any better if as good.  That was with carbon arrows.

[Swamp Yankee]

Make sure your have the calculator set up for -1/8 in the centercut; which is -3/16 actual centercut plus 1/16 for the arrow plate.

[Huntschool]

I am shooting AD's spined at .350 out of my MA and they fly great....

[metsastaja]

Noah, Im stumped. reran the numbers and your correct 20 some difference. Good luck

[nschlag]

thanks guys.

[Friend]

Stu's calc has been on the money for me when using round shafts and normal to hi FOC.
My bare shafted set-up on a former PSA was w/i two pounds.

Bare shafted tapered shafts would show some signifigant differences per the calc.

The 20#+ differences have been encountered for bare shafted mid to upper EFOC and Ultra-EFOC set-ups.

[Gray Buffalo]

It just might be your form. A friend had the same problem and we found he draw was not what he thought. He would creep forward before the shot causing the arrow to show stiff.

[BCWV]

I just put my numbers in Stu's calculator for my 50# PCH shooting woods. It's dead on.
 The bow was 63.4 and my arrow set up came out to 63.3. I don't know how to get a picture of the calculator in the post like you guys do!

[nschlag]

the calculator is spot on for my longbow. off like 3/10th of a pound. i have never found it accurate for my recurve though as it alway leaves my arrows overspined.

Gray Buff, i figured it must be a form issue. i have good anchor points and don't seem to be creeping. I will pay more attention to this.

Thanks again guys!

[Southern Sam]

I contacted stu about my psa also cause it came in way underspined about 13#.  He said the you need to put in .10 for the strike plate.  His calc already has the -3/16 in there but not the other for the calf hair and bump.  My psa does not like a stiff arrow either for some reason, but will shoot bareshaft, fletched and broadheads together.  I dont creep since ive checked it had others check me when i shoot.  So I'm leaving it alone.  Hope this helps!

[Bowmania]

I have always found the "cut to center" measurement to be a problem with Stu's.  Your measuring in two planes, so your kind of eyeing it.

Case in point.  I'm shooting a longbow 50 at 29.  Got pretty good flight with .500 which the calculator suggests.  For some reason I tried some .600's cut to 30 inches.  They fly great with get this 285 up front.  Paper tested with BH's from 15 feet to 20 yds.  go figure.

Bowmania

[nschlag]

Sam, thanks for the info.

Bowmania, sounds like some of my experiences.

I do love the calculator though. it has saved me lots of trial and error.

[ishoot4thrills]

Originally posted by Swamp Yankee:
Make sure your have the calculator set up for -1/8 in the centercut; which is -3/16 actual centercut plus 1/16 for the arrow plate.

Exactly. Or at least it needs to be very close because it makes a huge difference.

[lucky strike]

I  entered the input for 5 different bows-2 widow maII and 3 longbows 2 ff and 1 dacron .
All arrows I use for the different bows are dead on -bare shafted and paper tuned
Stu's chart shows all 5 bows need a spine apprx 20 lbs weaker than what I actually shoot.
When I tried the suggested shafts ,they all shot extremly weak with tears up to 3 inches.
I read about the personal form box and it assumes
that plucking woud be the reason for stiffer arrows being needed so I used a release aid to avoid that problem. The results were the same-the calculator spine suggestions were still apprx 20 lbs weak.
 I also checked the easton legacy chart and it also shows a 20 lb or so difference suggesting a shaft stiffer than the calculator