I prime on an RCBS bench primer and I was using and RCBS shell holder. It seems the RCBS shell holder opening for the case is slightly too big. When the case was fully against the back of the shell holder the primer and primer pocket were mot aligned. This caused metal on the edge of the primer to get shaved off and or the primer to not seat completely level. I had to carefully position each case and it was easy to mess up. I switched to a Hornady shell holder and problem solved. Now I can slam the case in there and it primes perfectly. I just use the RCBS shell holder for the amp annealer now. Hope this saves someone some trouble and wasted primers.