Briman

Here's another thought...I think you are definately heading down the right road.

The shellholders have slop in them, but not the 'right' kind of slop. If the shellholder isn't quite perfectly aligned with the ram below it, its going to force the brass into your sizing or seating die crooked.

Here's something I discovered by accident and much later read about it in Glen Zediker's "Reloading for Competition." I took my rockchucker press completely apart one day to clean all of the priming grit out of the ram and relube it. I broke the shellholder retaining spring in the process and never replaced it. I noticed when I put a shell in the holder and ran it into the sizing die, the shellholder will slide into a position that allows the brass to align with the die.

I read the same suggestion by Glen Zediker a few years later- he says to get rid of the shell holder retention spring as it can hold the shellholder in the wrong place and can put more pressure on one side of the holder than another, further exacerbating the problem. He reccommends buying a rubber O-ring to hold the shellholder in place because it allows plenty of play and is much more convenient than having to use a shellhold not held on to the ram with anything.