Looks like a Model VIII to me, and if there's no 70mm stamp on the flats, the chambers are almsot definitly 65 mm (2 1/2"). Someone's sure been inside the locks, may be only to replace a broken spring. I wouldn't use even low-pressure 2 3/4 shells in it, since older Sauers tend to have rather short forcing cones and the pressure rising effect of longer shells is the more noticable the shorter the cones are. Check out the condition of the wood, these guns "like" to develop cracks through the wrist with hot loads.
