Re: Shell holder Slop - how important is fit?
There's another important consideration (that's often overlooked) when switching to a different shellholder. You should accurately measure the distance between all three of a shellholders flat surfaces (top to center and overall height). I once discovered that when you switch shellholders, or use a different brand of shellholder, these dimensions can vary quite a bit. Even the slightest variation will affect all of your die settings.
Also, make sure your shellholder is clean so that you can push your case fully to the rear. This ensures that your resizing and bullet seating will "begin" with your case in a concentric alignment. These tips help to keep my case runout less than .002" (at the worst).