Strange Bow Tuning Question

[Tilzbow]

Okay, here's the set up. Same riser with different limbs. One set of limbs produces and 62" long recurve that draws 58# at 31" while the other set produces a 64" longbow w/carbon limbs that draws 50# at 31".

The 58# recurve limbs bare shaft tune with an Axis 300 w/225 (100 grain insert, 125 grain point) total grains up front or an Axis 340 with 140 grains (16 grain insert, 125 grain point) up front.

The 50# longbow limbs require an Axis 300 w/140 grains up front to bare shaft tune?!?!? If I shoot the Axis 340 with 140 grains up front from the 50# set up it impacts about 12" right at 20 yards indicating weak spine (what the???).

I solved the problem several months ago and I'm able to shoot both set ups just fine but I wouldn't expect these results!!!

Does anyone have any idea why 50# limbs would require such a heavier spined arrown than the 58# limbs on the same riser?????

....I have one theory but I don't want to let that one out just yet.....

[Str8Shooter]

I think that spine can be affected by the force that is applied at release and where it occurs. Say the 58# recurve limbs are very smooth and only gain 2-2.5# per inche towards the end where the LB limbs gain more, maybe3-3.5#. I would think on release the LB limbs would have a more abrubt launch and force the arrow to bend more as it goes through paradox. On the flip side the smoother limb may start accelerating the arrow more gradually inducing less paradox even though it is heavier.

Just a thought...

Chris

[Tilzbow]

Chris,

I've thought that same thing and it could be the reason. Anyone else want to take a guess?

[Tilzbow]

TTT

[Brian Krebs]

what was the barometric preasure; and humidity level; and temperature.. when the tests were done?

[legends1]

Just a thought,but do you think you maybe getting some finger pinch with the shorter limbs?May not be getting off the string as clean.

[Cherokee Scout]

A big factor could be string material may be different. String silencer placement, brace height can all impact spine. Also, you may not be pulling the exact same length with different poundages.

[Shawn Leonard]

If it is a hard R/D LB limb and carbon they may be better performers that the recurve limbs. I have owned a few LBs that at 5-8#s lighter than some of my recurves outperformed them consistently. Shawn

[JImmyDee]

When I first read this, I thought, "300s for a 58# bow?  I think those would be rather stiff!"

And I still think so.  I've got 340s flying out of a 60# @ 29-1/2" bow with 165gr points on the standard HIT inserts.  I've got 300s flying out of a 80# @ 29-1/2" bow with 250gr points on the standard HIT inserts.  I was able to get the stiffer shafts to fly from much lighter bows -- but then, stiff shafts generally do pretty well out of lighter bows.

One thing I find -- and I'd like to get corroboration -- is that carbon shafts seem to fly better out of longbows when they're "too long" by about 1-1/2".  How long are your arrows?

I suspect that you're shooting a center cut riser, right?  Is it cut so that you're past center with those skinny shafts?  Or is it on-center?