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

[lazyengineer]

Thank you. No extrusion evidence of gross overpressure. Solid primer strike with a deep impact, which you can only get in an AR15 with a fully rotated bolt. Brass blowout and peel back right at the seem between the web and the body. That brass failed because that brass wasn't supported by a steel chamber wall there. Meaning the chamber cut was too short (too much bevel), the brass head wasn't thick enough to cover that spot with strong enough solid brass head at that depth, or the bolt started unlocking and moving exposing that spot of the brass while still under pressure. Or a tolance stack of all 3 of those combine juuust enough, to kaboom. The correlation this seems to occur only with certain brands, is an item of note.

Section one of your lot of casings and another brand like Hornady, and take a hard look at the head, web, and transition between the two. And any different in how easy each was to cut.

You do you - I've seen this enough times now that when I pick up Lapua Grendel brass - I either scrap it, or run it as a mild fire/forget field load