It could be that the tubeset has a length of 66cm but I would ask for an image of the muzzle. Quality Krupp tubes by Louis Kelber. Proofmarks note constriction in the right tube. It is somewhat similar to the Sauer Modell 2 in some catalogues but I don't see any marks to suggest Sauer sourcing. But it is very similar to a F. W. Keler hammergun and I would say that components may have originated there and then a lesser known Suhl maker finished it for Kettner. The image of the toplever has the Greener crossbolt out and it is not in battery and that is why the toplever is to the right. Appears to be a upper rung hammergun offering made between 1912 & 1923.
Kind Regards,
Raimey
rse
