I got some from a friend who thought they were overspined for his bow. They should be overspined for mine too, but they shoot so well I really don't care. I did check them on my homemade spine tester. They were much more consistent than my other carbons, but not as good as ACCs. They still shoot very well, as well as the ACCs for me. I guess my shooting ability is not good enough to tell the difference. They shoot broadheads spot on with my field points out to 40 yards, and well enough that I'm taking a risk by shooting 2 at the same spot. (Havent destroyed any arrows, but have had to refletch.) The ones I have are only the Cheetah hunters, not the better grade ones. These are the only .006 carbons I've had where is seems all 12 shoot well. I guess you can tell I'm impressed. I originally was going to sell these 55-80s and get either 45-70s or CT Whitetails. I just can't see getting rid of them the way they shoot.