My 1:9 twist was sufficient to stabilize the 170 gr Berger. The cow elk was quartering towards me at 250yds. The projectile broke through the rib behind the shoulder and travelled diagonally breaking the off side rib and stopped just under the skin. The cow elk took two steps and dropped. The projectile had about 10-20% weight retention with Significant internal damage. This is my go to bullet with a MV of 3015