This was something I kinda got forced into back in the 60's. My first set of dies were hand dies for the .303 British. One of the older sages in my home town offered me an upgrade - an ancient Lyman press for free - only problem was that it had a little alignment problem. Only way to seat bullets reasonably straight was to do it in about four steps; rotating the case each time about 1/4 turn.

On the oversize shellholder, I generally use a .308 shellholder for the 6MM PPC, and a .220 Swift shellholder for seating rounds with the .308/30/06 case head. They fit loose enough so the round is going to find the center of the seater die without any interference from the shellholder - but still hang onto the case just enough so it isn't going to fall out of the shellholder. Roskoe