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

[LRRPF52]

I went through the same process when I first started loading for Grendel, without any failures though.

The shiny ring you see is the web area. The case walls forward of that actually expand into the chamber walls, then rebound a little.

Everything gets put back into place when you properly re-size the brass, using consistent case lube and minimal movement of the headspace to allow reliable feeding in your chamber.

You can see the same surface contrast on other cases too, including 6.5x55 Mauser, .260 Remington, 6.5x47 Lapua, 6.5 Grendel, 6mm-AR, and .308 Winchester:

(These have all been polished, so the presence of the ring varies in appearance.)