So i have read on a few different forums that the last shot from an AR when the bolt locks back will stray slightly from the others. I read this when people have been talking about shooting groups and the last round will fly off by 1/2" or so from the others because the harmonics differ when the bolt locks back instead of chambering another round. I dont see how this is as the bullet has already left the barrel before any of this happens. Could someone explain this? Thanks.