ASTM standards? for arrow spine

[Adrian Farmer]

I recently had an experience with carbon arrow selection that has taken me aback.  The background.  I am shooting a new bow – DAS/Dalaa takedown recurve, 55# @ 28”, with carbon/foam limbs.  I draw about 29”.  I have tentatively selected two shafts to evaluate:

1) Alaska Bowhunter’s Momentum (6580), cut to 30” with 4-4” fletching.  This is a tapered shaft with an advertised deflection of .330.  With a 250 grain point, this arrow shoots great (and bare shafts well) out of my new bow, but is on the margin of being too weak.  

2)  Arrow Dynamics Traditional.  A tapered shaft cut and fletched the same as above; advertised as having a deflection of .275.  With a 250 grain point it also flies well but is on the verge of being too stiff.  

Given the above results, I decided to try an Easton Axis Nano 300 shaft with an advertised deflection of .300 (that is, right in the mid-range between the two shafts above!).  Cut to the same length, fletched similarly, and with a 250 grain point, however, it is way too stiff!  

Why these results?  This indicates that the so-called standards are not really all that standard among manufacturers.  I near as I could determine, all the shafts were measured with the ASTM standard, but perhaps this in not true.  Perhaps in this case it’s due to comparing tapered shafts against a parallel shaft, combined with the fact that the deflection of a tapered shaft depends on how the manufacturer positions the shaft on the spine tester.  In any event I am stymied and hesitant to do more experimentation based on the rated deflection number.   Any ideas?

[JRY309]

I find you can't compare the spines listed for a tapered carbon with a parallel carbon.I shoot the AD Trad out of my 58#@27 longbow,but with a parallel carbon I'll shoot a .400 spine arrow.Tapered carbons seem to be more forgiving,I can change the point weight as much as 50 grs. and they will still group together.This has been my experience with tapered carbons.

[wtpops]

One thing you may have to take into account is the nano is more than likely less than 1/2 the diameter of the other two shafts at the point end and may put the arrow on the wrong side of center of the string. If you are shooting off the shelf and sight window you may need to build out the strike plate a little. I know is sounds strange but if that nano is sitting past center on the wrong side of the string i will cause strange flight.

JEY309 has a point also, those tapered carbons are strange critters when it comes to spine

[Adrian Farmer]

Rick:

I can adjust the centershot on my bow.  I tried to set  the arrow rest at the same relative location for all three shafts; hence I adjusted the rest outward for the Easton nano.  If I had not done this, however, the nano would have been way inside of centershot, as you point out, but that position would have made it shoot weaker (not stronger).  At this point, I would tentatively conclude that the difference in dynamic spine has to do with arrow design (tapered vs, parallel).  Interesting the difference that that makes!