Both M1 and M14/M1A rifles can fire out of battery even though the hammer is still held back by the sear. Extra thin/soft primer cups will fire the round by the inertia of the firing pin before the bolt's closed full into battery.
Search this forum for "slamfire M1A" and several links to discussions will show up. Member "Slamfire" has a lot of good info on such things.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master
Last edited by Bart B.; October 14, 2013 at 04:19 PM.