1/9 twist And why the different grain bullets heck I don't know on the side of the mountain I live I have maybe seen 2 coyotes but lots of bob cats on the other side of the mountain in eastern Oregon I see coyotes all the time when Elk hunting but they are usually out of bow range. Just figured use a smaller bullet for the cats and little bigger for coyotes. Never shot either yet with my AR so not sure how devastating the Ammo would be. New to the predator hunting scene.