I have just started reloading .223/5.56. I have found that some - a noticeable number but far less than half - of the brass that I'm using has a primer pocket that is too small to accept small rifle primers from both Federal and CCI. There does not appear to be any particular brand correlation. All of my brass is saved from factory loads that have been shot from my rifle. Does anyone know why some of the primer pockets are smaller?