I'll vote with Raimey on the rifle caliber. The chamber may or may not have "modern" .360 2-1/4" (9,3x57R) dimensions so a chamber cast is a must. Bore and groove dimensions will just be what they will be.
Crown-over-G (gezeugen) rifled bore, eagle with crown-over-U final inspection, crown-over-S smoothbore, no nitro marks. Crown-over-C ??? I'd love to see a picture of the flats. The 118/35 gauge mark is pretty much indicative of 1892-1912 manufacture which will hardly surprise you.
I'm guessing that this is a side-by-side "Cape" gun rather than and over-under "Combo" gun, yes?
