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

[Klem]

I would expect more soot regardless of failure cause than is pictured.

Maybe - not if it was expanded and sealed forward of the rupture as it should, and it was a relatively new case. The soot coming out of the rupture gets focussed back past the bolt to the magazine.

If a suppressor was on it then all the spents would be filthy, as it all comes back from the chamber as the case contracts.