Lrf,

I have some 8x57R, someone else on the site may be able to confirm this but, I believe you can run the 8x57r brass into a 7x57 sizing die and end up with what you need. If you are close enough to pick it up I can spare half a dozen rounds of brass if you like. Would make headspacing a lot easier with actual brass rather than just dimensions...

I looked but unfortunately do not have a set of 7x57mm dies or I would lend you those.

WBLDon