[johndallman]

Originally Posted by Icelander

Does anyone know how common the Mannlicher-Schönauer Grosswildbüchse rifle might be in 1944-1945?

Very rare, I think.

If the leadership of the SS were quietly preparing to escape to another world with the defeat of the German Reich, could they surreptitiously obtain a few of them?

Maybe. Two or three? Probably not more. A place where you might well find one would be Carinhall, since the guns from Reichsjägerhof Rominten would likely have been taken there after the hunting lodge was demolished.

If any of the Austrian nobility or wealthy industrialists who owned such a rifle before the Anschluss were politically unreliable or even, gasp, of impure racial stock, it might well be that their rifles had already been seized by German security services, in which case the SS would presumably find them easy enough to obtain.

Except that SS members would probably have stolen them at the time of seizure.

… if someone living under the regime of the Third Reich owned a rifle in 12.7x70mmRB, it was more likely to be a Mauser 98 pattern.

Since one of the main points of creating the cartridge was to get a stupidly powerful big-game cartridge that would fit in a standard size Mauser 1898 action, that's much more likely. And building guns like that in exile makes far more sense than small-scale manufacture of a different rifle.

The British version, using a Mauser 1898 action, has Shots 3+1: I dug up a copy of the manufacturer's catalog, and worked up GURPS stats. They also need to bring dies and tools for making 12.7x70RB ammunition.