Though I said this project would be put on hold till we return from our road trip, it has kept gnawing at me, so I got back to it.
First, removing the extractor didn't make any difference.
Next, per Ian’s suggestion, I dabbed a bit beeswax between the neck/shoulder area, and it smeared a lot. I tried ever decreasing dabs, but the smear was always larger than the dab. No headspace?
99% of my press usage is with the Lee 4-hole turret, with it’s dead stop design. However, Allen’s mention of adjusting the full length die so the press cams over, was the nudge for me to try it with the RCBS Jr 3. I gradually turned the die in till a case could be chambered with just the slightest bit of resistance increase, over that required when closing the bolt on an empty chamber. A wee dab of beeswax showed only a very, very slight smear.
Ah, ha, success!
That lasted till I turned the die in the next little bit and stuck a case. Cleared that fiasco, backed out the die a bit, but not too far enough and stuck another case. Fixed that and called it quits . . .
Never experiencing this problem before, it seems to me that some brand of shoulder set-back die is needed. (Isn't that what you mentioned, Ian?) If that is correct (please say so if it’s not), I will gladly entertain suggestions.