The reason for the need to trim the .25 ACP brass is that I'm using a .25 ACP breech plug conversion on a T/C Omega. You use primed .25 ACP brass instead of a 209 shotgun primer for ignition. The lockup on the action is very hard, harder than is necessary. If I could trim 2-3 thousandths off the brass, then the lockup on the action would take much less pressure to close.