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

[LRRPF52]

Again, the chamber wall is supporting the other theoretical end, so there is no blown out brass there. That's why there is a clean tear there that matches the consistent score line position. This matches theory. The blowout and brass damage is only occurring at the unsupported area which is at the feed cone. This is what I see in the pics.

There’s nothing theoretical about the brass being supported in that location. It either was or it wasn’t.

If the feed cone was the factor, then we should see circumferential and relatively-even failure with a total case head separation.

Instead, we just happen to see it fail aligned perfectly with axial extractor force.

We also don’t see evidence of catastrophic failure of the surrounding pressure containment structures and the non-pressure-bearing structures that hold them.

I would suggest more study of AR-15 catastrophic malfunctions, brass yield strength, and what those look like.