First time I found one of these I also wondered if the idea was to prevent bullet setback, because if that is the idea -- the idea itself is sound. Not sure about the execution of the idea and for a handloader, this is a very obvious pressure raising situation.
I also cull all of these from my brass supply, but this is not at all difficult for me since I sort all handgun brass by headstamp anyway.
Fantastic pictures and sectioning, OP!
