I'm assuming its an M1A and not a real M14? Try only a full length, re-sized case. Also, is it a National Match, Super match or such, with a MATCH chamber? If it's a Springfield, they can have very close tolerances on the chamber fit. They even come with a card stating the chamber tolerance. Mine would even chamber some Mil-Surp ammo--it would only take really nice, full-length sized handloads or US Match 308 ammo, but that's what I got it for. Good luck.