I been working on a load for my 12F in .308 and a guy at the range gave me 500 rounds on WIN supreme match brass that was shot one time out of a 700 Rem from the police dept. After cleaning and full resizing, trim to lenght. I loaded it with 42gr of reloader 15 and push in 168gr sierra MK it shot fine but some of the loads the brass was damaged at the shoulder? All the rest of my loads where fine. I use lupua brass mainly. I check the chamber and it checked fine?? Am I missing something?