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Arrow spine after cutting?

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5.5K views 6 replies 5 participants last post by  Flatwoodshunter  
R
#1 ·
So Im still relatively new to bow hunting, this will be my 3rd season with a bow.
I have been trying to learn a little more about my equipment and how to improve accuracy and consistency.
One thing I was curious about was, when you cut an arrow your increasing the spine/stiffness. But is there an equation or rule of thumb as to how much this spine increases per .5" ?
I currently shoot a Nitrum turbo with 70lb limbs, turned down to 62lb, with a 29.5" draw. With a lot of stock arrows coming stock at 31", that's a solid 2 or 2.5" being cut off. Is this a significant increase in spine or am I fine as long as I follow manufacturer charts?
 
#3 ·
I've recently gone 2.5 inches less than full length shafts and noticed a big difference in tuning going from a 1.5 inch tear to near bullet holes on the same spec bow setup. Even added another 25g up front and tuning didn't change. This was with new arrows at same gpi and spine but much better tolerance spec so not sure if that played a role in it.
 
#5 ·
Nitrum Turbo
62 lbs draw weight
29.5-inch draw length

Use 300 spine rating arrow
Cut the arrow tubes to 29-inches from end of carbon tube to end of carbon tube
INstall the insert and use 125 grain field points
Blazer vanes

This should work nicely for you.

Arrows rated at 300 spine, have the supports 28-inches apart. 300 spine means the arrow will bend 0.300 inches at the middle of the arrow tube,
when the spine testing supports are 28-inches apart. IF the arrow tubes are 31-inches long, the STATIC deflection rating is 300 spine. If you cut the arrow tubes to 29-inches long, the STATIC deflection rating is still 300 spine. If you cut the Tubes to 10-inches long, the STATIC deflection rating is still 300 spine.

Yes, of course, a full length 300 spine rating arrow at 31-inch long tubes is a more flexible behaving arrow. This is DYNAMIC arrow behavior. So, if you cut the 300 spine rating arrow at 29-inch long tubes, now the 300 spine rating arrow behaves STIFFER. If you cut the 300 spine rating arrow at 28-inch long tubes, now the 300 spine rating arrow behaves even STIFFER. You can use 100 grain screw in field points, and the 29-inch long 300 spine rating arrow tubes will behave STIFFER. If you use 150 grain screw in field points, with the 29-inch long 300 spine rating arrow tubes, the arrows will behave WEAKER. Spine rating on your tubes never change.
 
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