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arrow spine

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WhistlingBadger:
I think you're all correct; spine does matter.  But I would add that Ryan Gill isn't some newby know-it-all.  He has probably forgotten more about primitive archery than I will ever know, killed dozens of animals with primitive gear, from small game up to bison, is consulted by university anthropology departments.  When he makes a claim I sit up and take notice, even if I don't understand it or it goes against what I know. 

I certainly wouldn't dismiss anything he says as nonsense without at least watching the video.  There's a lot more to it than "arrow spine doesn't matter."

Chumash:
The important word is "SOMETIMES" and Ryan explains in the video what this "SOMETIMES" is, for him and his experiences.

Tuomo:
Spine does matter!
If you’ve ever shot a bare-shaft test, you know it absolutely matters. And using a bare-shaft test is the only reliable way to determine the correct arrow parameters—it immediately shows whether an arrow is dynamically correct, too weak, or too stiff.

The old rule of 5# per inch of arrow length applies only when the bow’s draw weight is around 65–75#. The rule was “created” by Saxton Pope, who shot bows in that range. For weaker bows, the rule simply doesn’t hold. In reality, the correlation is non-linear. For example, with 35–40# bows, the “rule” is roughly 2.5# per inch. And so on.

It’s also commonly assumed that a 28" arrow requires spine matching the bow weight—for example, a 30# bow needs a 30# arrow. But again, in practice this varies from archer to archer. One shooter may need 35# or even 40# arrows, while another may need 25# arrows for the same 30# bow. A bare shaft test will tell the truth.

The cut-in window has no effect. The required arrow spine is the same for wide-handle bows, narrow-handle bows, or windowed bows. If you don’t believe it, do a bare-shaft test using the same bow with different handle widths.

And finally, arrow point weight has almost no effect on required shaft spine. A 25-grain change influences spine by about 1# or less. Again—shoot a bare-shaft test to see for yourself!

bassman211:
Cut in window has no effect. Must be me, and thousands of other guys that know the closer to center shot the easier it is to tune a bare shaft of one , and some times 2 spines. Congrads on winning the bow of the month. Nice work.

Tuomo:
A cut-in window has no effect on the optimal spine of the arrow. You can verify this with a bare-shaft test if you don’t believe it. However, the cut-in window does make arrows less sensitive to spine variation. With a cut-in window, tuning and shooting become easier because the arrows are less affected by spine variation, release inconsistencies, or other tuning issues. The wider the handle, the more sensitive everything becomes.

My point is that if the optimal static spine is, for example, 42#, it remains the same regardless of the handle width. But with a wide-handle bow, a 44# bare-shaft arrow may fly to the left (for a right-handed shooter), while with a cut-in window the same arrow may still fly straight.

Regarding the “correct” spine, it’s more of a statistical issue. I can shoot accurately with normal, fletched arrows even when the spine variation within the set is 10–15#. But arrows that don’t have the optimal spine will occasionally fly farther left or right. Over the long term, statistically, the arrows with the correct spine will land in the center most consistently. Again, it comes down to sensitivity to various factors (spine, bow, archer, etc.).

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