Since you state that the casings will only be fired in your rifle alone, I recommend that you set your resize die to size the neck and only very lightly touch the shoulder of the casing. The method I use is to back your resize die way off, use a candle or other flame source and coat the neck and shoulder of the casing with soot from the flame. When cool, run the casing into the resize die and by lowering it until it just barely takes the soot off the shoulder, you have set that die for that chamber of that gun. Naturally, this must be done with a casing previously fired in that particular gun.