This one's just marked 8,57 (I should have said it was a model S to avoid confusion). Measuring the groove diameter at the barrel gave me the .316 reading before. That didn't sound right, so I slugged the barrel and the thumb dial digital micrometer gave a more accurate measure (.32145).

I haven't had the stock off yet, but will find out what's on the underside of the barrel shank while it's in the shop.

A chamber cast showed that the chamber was normal (not short) for the 8x57, so I'm thinking that the brass has to be flowing into the barrel. The primers looked normal; the main difference seems to be that the PPU brass was visibly annealed and appeared thinner at the neck. If it turns out to be a pressure issue or it's marked for the smaller bullets, I'll load .318 200 grainers.