if full length sizing, you don' t want to back it out with most dies, but screw in more to cam down on the piston. After touching the piston at the top of the stroke, you want to screw in another 1/8 to 1/4" . What I mean by fireformed, is was they shot in your gun then you reloaded them. I thought you might be getting brass from someone else that was shot. Try screwing in that dies more. That should move your shoulder back. Also what another guy said about trimming is important also.