[Unclenick]

Still might get better rigidity if you built up some shims to fill the gap between the bottom of the die and the shell holder. Shim washers would work in lieu of the Redding shell holders, but first you'd have to locate some the right size.

Still seems odd to get that much difference; a 0.009" span. Hmmm. From PA-Joe's point, is there any chance lube is squirting up the sides and into the shoulder area between the case and the die? As an experiment, you could try Q-tipping the lube out of the die shoulder area just before each sizing.

Another thought is to try my trick for hard-to-resize cases of letting the case sit in the size five seconds with the ram up, withdrawing, rotating 180° and doing it again. The idea is to give the brass a little time to stress-relieve inside the die. Chances are they will all come out a little shorter, but shorter and the same is better than different lengths because you can adjust the die to compensate on the next round.

You could also try annealing necks and shoulders, but it is so easy not to get that exactly the same on each case that it may help or it may worsen the situation. If you choose to try, I would use one of the slower, more controlled temperature methods (e.g., hold in fingers and rotate neck and shoulder back and forth in a candle flame until it gets too hot to hang onto, then drop into water or onto a damp rag with a twist; rub soot off later with steel wool or tumble).