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

[LRRPF52]

Yes - the extractor was in good shape, but the bolt was out of spec after this firing per seating the no-go gauge.

The more I have thought about this since yesterday, the more I am wondering about the bolt face depth.

If you had an out-of-spec bolt face depth that exceeds .136”, and a properly-cut chamber, it could also cause this to happen.

The fact that your extractor is intact, there aren’t any ejector extrusion marks or extractor pocket ledge shearing, and primer has a nice dimple on it all point to a well-within normal chamber pressure.

The flat primer is often seen in excessive headspace, when the primer backs out and slams against the bolt face, followed by the case re-seating over it due to brass expansion.

I need to go look at your headspace measurements again.

"Note: all these (2.246 - 2.26) may be too long for throat length. In the 123 Hornady BTHP, I had bullets possibly stick in the lands and had click-no-bang, and then trouble extracting the unfired cartridge"

At the time, I theorized that it was a jam into lands issue, but this didn't exactly line up after I got the Hornady COL gauge which found jam length of 2.3050 for the HPBT and 2.310 for the ELD-M.

It is interesting that I've only noticed the ring on one other case out of the 40+ I've shot in that batch so far. Next step is actually measure the powder from a few rounds when I get my puller...

Click-no-bang is a telltale sign of excess headspace.

Firing pin hits the primer, which just pushes the floating cartridge forward in the chamber without activating the primer.