Hello all.
I am still going to stick with what Rob and I looked at which is that the lower part of the case below the very long neck is concave. I remember reading somewhere that this was something that was not uncommon. I think that I actually saw diagrams from older German cartridge lists that showed this as well. Regardless, I could be imagining all of it.
M-4, agreed that the cost of a reamer (and changing the rifle) is about the same as having dies cut to match the chamber. It is easy enough to thin the rims on the lathe as well.
But as Kuduae said, many of those rifles were normalized while still in Europe, so who knows how many aren't in original condition.
Kuduae, were there nitro versions of the older chamberings? This one is nitro proofed.
Last, whose proofmark is a crown over a B?
Tom
