Guess we'll have to agree to disagree on this one. I couldn't give a physics formula to explain they how's and why's, but I can say, from experience, that some arrows in a given spine have not flown the same as other arrows in the same spine, but a different material.

For instance, when I shot ash arrows I had to go up in spine. I have a couple of theories, but nothing solid except the results I got. Possibly the heavier over-all weight of the shaft acted somewhat like a heavier point; or maybe the recovery time was slower; or it could be some other factor-- but that's the way it worked for me.

I think the point Jakes was trying to make (correct me if I'm wrong Jakes) is that there are some variables that you cannot predict, primarily release. Take two people with identical bows and identical draw lengths, and they may still need different spined arrows if there is a big difference in their release. However, it shouldn't be a big difference in the arrow spine they need, so the "if it works for me, it should work for you" will normally get you in the ball park. Nobody can say exactly what spine will work best on a given bow every time, because you can't put a formula on an individual's release.

A pound of feathers weighs the same as a pound of steel, but there is a difference. If you don't think so, drop each one from 6 feet onto your big toe and see it that doesn't change your mind.

Chad