Using both new (Winchester) and once fired (Remington) brass, with necks chamfered, I experienced some case shoulder crushing and slight bulging when seating flat based Hornady V-Max 55 grain bullets in the RCBS seating die.
The Remington cases were factory annealed, once fired in my M-4, full length sized along with the new Winchester cases, and not all of the Remington cases "crushed", but about 18 did out of say 60, and for no apparent reason.
The slightly "crushed" cases seem to cycle through the M-4 receiver, chamber OK, extract unfired OK, and I preceive teh M-4 to be one stout rifle.
It is wondered if others have had any similar circumstances?