I actually did testing shooting through bottles stuffed with wet rags and found tumbling was a sigificant issue with 6.5 copper bullets. The higher the grain the more likely to have a problem. I was shooting a 1 in 9 twist and Steve at Hammer told me to stick to 125 grain. I did and still had the tumblng issues. I switched to Barnes 125 and did not have that issue but the barnes did not shoot as accurately as the hammers in that rifle. I decided if I want to shoot non lead bullets then I'm not going to use 6.5 caliber. I got a 280 AI and the difference is substantial.