Cleaned my Ruger MK2 tonight , put the barrel on , put the bolt in pointed it up pulled the trigger ,put the retainer in, pointed it down pulled the trigger and snapped the catch in . Pulled the bolt back and dry fired it . Looked down and there was the firing pin retainer pin on the bench. Took it back down and the dent was there in the breech face .Took out my needle files and smoothed it out, half round for the chamber and flat for the barrel face.Put 5 in the mag and cycled them through the gun and looked at the rounds ,no marks. My question is , if I'm going to have a problem what should I look for?