Admittedly, I have only shot South African military ball, in their thousands through my LE, and unfortunately too little through the last 303 Brens in SA service. Ammo dated from 1943 to 1945 in the Bren in 1972. Others dated from 1956 onwards in my LE. Never seen any kind of crimp in any of the lots. Doesn't mean it wasn't done, just that it wasn't visible.