Thanks for all your help. I was playing with my dies tonight, and I want to be sure I understand.

I used the "butane smudge" method, and continued to screw the die in until I "scraped off" the entire neck. Is that correct?

As a "test", I found one round I did previously with no primer (I needed a dummy round to check COL), smudged that one, and ran that through the die. It's difficult to see (perhaps only a few thousandths), but it looks like there is still "neck" left un-smudged.

So if I'm understanding this correctly, I pushed the shoulder back too far. The round chambered, but I had too much headspace. Not enough to split the case, but certainly enough for over-pressure.

Am I correct in my hypothesis?

With this in mind, I need to full length form the brass I'd already sized too deeply, correct?

Perhaps I should just quit neck sizing, and only full length size?

Final question: I have a few of my previously loaded rounds. I pulled the projectile, emptied the powder, but they are still primed.

Choice: Full Length size with no de-capping pin, or simply fire off the primers at the range and start over.

I have so many questions!