Ok, my friend and I went shooting his AR-180 today, and when we looked at the targets, the hits had the distictive "keyhole" shape of tumbling bullets. We'd seen it before when shooting through multiple layers of targets, but this was a clear shot. The bullets used were 62gr FMJ boat-tail and SS109, both facory and handloads with 25gr of IMR 4320. We figured it was because of the 1/12 rifling of the 180, as I'm told the SS109 should use 1/7 rifling. Anyone know more about this?