I was having same issue with the 450's. I think i have it resolved. I was making brass converted to 6x45. most would fire but having alot of failures. I ended up not FL sizing the brass, just sized enough of the necks for bullet tension. Bold is snug to close due to not pushing shoulder back. So far that has fixed issue. Im still forming brass. I would measure your sized brass piece by piece and see what they are reading. Thats how i found my issue.