With a slight neck size, I doubt the case is lengthening.

I'm putting my money on the cases bulging in the seating die. That can be a real bugger. JMO, Dutch.

I had a similar experience. In my case, however, even full length resizing moved the shoulder forward .001" to .002" (based on headspace measurement of an RCBS Precision Mic) for the reason 'Ol Joe cites. It turned out the FL die wasn't touching the shoulder, even when the base of the die rested against the shellholder. It "squeezed" the case itself, and the extra brass became more shoulder length (also known as "less headspace"). I sent the die back to the maker to have the die based milled down a few thousandths. I sent them a fired case and told them I wanted it back .002 past that. That worked fine.

Jaywalker

camberfer the necks...

i'll bet that the neck is the issue... what could haev happened, if you don't apply a crimp, if the brass could have a square edge on the throat, that is preventing the round from entering the chamber.

(dismantle first) and then LIGHTLY crimp a couple...

bet it fits
jeffe

I have Buldged the shoulder before while seating or crimping. It is very hard to see unless you mike it but, it can really cause some frustration.

You may want to check the measurements on your shoulder dia. Also, as other have mentioned, sometimes when partial FL sizing the neck will scoot foward on ya causing the improper angle and the rounds to be stiff. I prefer to completely FL so that the die bumps the shoulder or to just neck size.

Good Luck!

Reloader