Carhub48,
The photos confirm the rifle barrel is chambered for 9.3x72R, but rather than copper jacked bullet (KmG), it was proofed for a 13 gram lead (Bl.G) bullet. It was nitro proofed in Suhl ( shown by "nitro" being written in block letters) after 1911, as stated before, and before 1923, when Suhl started dating the proof. The 16 in a circle means it was proofed with the standard 16 ga. chamber, which was 2 1/2- 2 9/16" instead of todays American standard of 2 3/4". The 16, no circle, is the diameter of the shotgun barrels, ahead of the chamber, expressed in gauge measurement. The crown W means the shotgun barrel that has this mark is "choked", but the degree of constriction is not shown. The crown U, with eagle, is the mark for" View" proof, which was basically a detailed inspection, including verification of dimensions, after firing the final proof load. There was no photo, but the shot barrels were likely marked with a crown S, which shows the barrels were proofed to fire shot. I hope you find this helpful.
Mike
