Without more information this would seem to be one of two things. You have loose primer pockets (not likely since it happened with different lots of brass) or you are running into high pressure for some reason.
There is a third reason and that would be badly dished out bolt face allowing the primer to be forced back against the bolt face when fired and the differences you see in measurements with different brass would be due to how tight the primer pocket is.
My money would be on the high pressure.
Gary
Bookmarks