Agree with the above. When I got my M1, CCI 34s were unobtanium. Still are. I went with Winchester LR with no problems whatsoever. That said, one must pay close attention to seating depth. They MUST be seated a couple thou below the case head. In prepping my cases, I use a Sinclair primer pocket uniformer. It is amazing how much brass comes out of some of them. I also hand prime, so I can feel each primer seat and then feel the primer to ensure its seated properly. Anal? Probably, but its worked for me for many 100s of rounds.