Wow. I've never seen a tighter primer pocket. I ruined 6 210M's before I got the hang of it with an RCBS hand priming tool. I found that if I held the case against the back of the shell plate they seated fine, but if the primer got cockeyed just the slightest bit the primer deformed. I guess I got too used to RP brass in my .260. NOTE: I'm not saying this is a bad thing, in fact I am very happy that the primer pockets are tight. However, there is a learning curve.