Appears this gun has a mixture of proofs. Part are Birmingham, part are non-English. In the days this gun was built there would be no Metric marks on a Birmingham proofed gun, & "NICHT FUR KUGEL" sounds German. 17/1 would have been the Birmingham mark for a bore which wouild take a .656" Dia plug but not a .662" one. 16.8MM = .661" which sounds like a 16ga bore dia, but have never seen a C in front of a bore marking. The 1,326G would be the wt of the bbls in grams (2.92lbs) but this is also not an English mark.
