Mike,those are the 280's I know off as well.
Thanks for providing the rim diameters.
The pleasures of vintage rifles indeed. I had a lovely Schmidt and Habermann Mauser in 9.3x64, a dream rifle, at least for me. Sadly the bolt face which should have been 12.65mm diameter was in fact 12.0mm (0.472”, standard for a 9.3 x 57, 9.3 x 62, .308win etc etc). No wonder my RWS ammo would not chamber. My suspicion at the time was that someone replaced the original bolt with a generic Mauser one. Could that have happened on this rifle as well? In which case, unlucky me.