Q for those more expert than myself

[angrybear]

If you're using dies that rely on the neck meeting the die (lee combine crimp and seat die for example) then I can see how this would happen. I much prefer the dead length seater die as the shell holder meeting the base of the die is a definite stop and leads to more uniform loads.

I would trim them all to the same length and load but do a couple of pressure loads at .5 / .2 gr under as you'll be eating up case capacity. Have they shrunk through fire forming?

I suspect so.

Did you re-size the empty cases before measuring them?

Yes, neck sized, RCBS if it matters