Vic,
I have to lean toward a faulty breechblock from a metallurgy standpoint(possibly a heat treatment issue). I am at a loss as to what else could cause this. There is a very strong chance that with this condition, and continued firing, that the two elevated areas on each side of the extractor channel will break off. There is a photo of a breechblock doing this very thing on this forum.....I can't remember exactly where I saw it. I really wish that I could be more help to you.
