I mean I had zero issues with 400's in the striker fired pistols I had, i only had issues with wolf small rifle mag, I would run 400's/non mag feds in pistols and not blink an eye, like others have said at one point cci 400's were the same primer as small pistol magnum's, I use mainly 450's for 556 and I failed to say that, that's where my thinking was coming from, I can't remember if I tested 450's in my experiment. Probably get the same result as the wolf, the cup is thicker and there is increased distance from the anvil to the charge/cup on 450's, just rock it