I had a partial case head separation using a 1.8oz buffer

[DeNinny]

None of that approach is applicable though, since you don’t know how far the case was extracted already when the partial head separation occurred.

It's applicable because my model is an in battery blowout. I never said the case was being extracted because it doesn't need to be. Not even partially. It already has unsupported sidewall without having to move! And this is something Bill Alexander himself acknowledged and addressed in his grendel barrel design. He shrank the overall size of the feed cone so there's more supported wall as compared to the M16 feed cone.

We are literally staring at a failure that Bill Alexander himself designed around. Because he knew it was an issue.

The side wall growth with that line is indicative of residual pressure on the case walls with a case that is already being extracted, not one that’s in battery.

I disagree. It's exactly indicative of the point where the feed cone starts inside the chamber. While in battery, the brass is literally bending and forming the score line where the chamber wall ends and the feed cone starts (at that end).

This is again a textbook sign of early extraction, bad timing of the system.

This is again a textbook example of a case head expanding into the unsupported wall area of the barrel which is the feed cone. Two rounds expanded and deformed without blowing out. The third one did.