Re: Mix and Match die use
I done "mix and match" for a long time. Purchase a new set for a new caliber (Man, I haven't done that for a long time now!) Then, as I get a chance to pick up a different set, I keep the keepers and sell the losers.
I make casts of my chambers and compare the casts to my FL sizers, or at least to the cases sized by them. Those dies that (1) best match my chamber and (2) make the straightest necks are keepers.
Used to try seaters that way too but in recent years I've just gone to Forster BR seaters, saves time and I never lose.
Neck sizing is always done with a Lee Collet die, period.
Accuracy cases that are FL sized are ONLY expanded with a Lyman "M" type expander, I no longer use conventional expander balls. Not since I got a concentricity gage anyway!
Crimping, if any, is with a Lee Factory Crimp Die (FCD).