Sounds like a hot load was the problem, not the headspace. Did you measure the jump or did you jam the bullet?
Yes and no. The hot load was clearly the problem, but it was also one of a couple. And yes, I did set he seating by the marked bullet, seating progressively shorter method.
BUT, it had also been done before the barrel came off and went back on. As I said above, overconfidence had gotten the better of me. One round was on the hot side, the second was beyond hot, and I halted immediately. The headspace also was a factor because the resulting chamber was shorter, increasing gas pressure. Also, the bullet was considerably longer, and was taking up more case capacity. It was a perfect storm of assumptions and consequences. I thought I had reduced the charge far enough, but I had still gotten it wrong.
I had been in a similar situation losing primers two decades earlier during a match over a thousand miles from home, firing ammo made up by someone else. So I was able to recognize the issue immediately and halt any further firing.
It was a number of lessons learned the hard way.
FWIW, I still hope to develop a load for the ELD-X but that's been put back into the queue at a lower priority. I'm continuing the initial project with the Speer Gold Dot bullet, which packs terminal performance, and acceptable (if somewhat lower BC) into a far shorter package with siginificantly less case intrusion.
I was being dumb, and pointing out how this could happen was the main point of my post. I am hoping to spare others a similar experience.
Greg