Maybe not quite so elegant a fix as machining the stem, but I've used epoxy and a lubed ELDM/X bullet to match my seating stem to the ogive, works gud
As for 'micro adjust', I load up a dummy/reference round and crimp the bullet in a bit tighter than usual (checking OAL not altered) then each time I need to replicate that load, just wind out the finger adjustable part of the seating die, raise the ram all the way, and then screw the adjuster back down till in firm contact with the reference round.
Been very accurate for me, cheap too!
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