I believe you are looking at what would be a 9.3x72 in our terminology.

The only way to be absolutely sure will be to do a chamber cast and slug the barrel.

I will ask next time I go there. I am not certain the owner brought the rifle in with him.

This leads to the question - is the cartridge case rimmed or rimless ? If it is rimmed it could be one of the following calibres -8 x 72R Nimrod ; 8 x 72R Collath ; 8 x 72R Teschner ; 8 x 72R/360 ; 8.2 x 72R . Or a 9 mm variant as suggested , there are more 9mm variants than 8mm .

It is unlikely to be a rimless calibre in the size mentioned anyway , but once again without the actual referance we are all just guessing

Are you saying it is not a bochsb... because the rifle bbl is situated over the shot bbl? If so what do you call it? It is most possible that my memory from 25 yrs ago is very poor. I know drilling and vierling and that I am sure of. All else is is followed by ????. Thanx for reply. I never thought about bore diameter. I have read it before just did not recall untill mentioned. Wierd stuff shows up here ocassionally. Always interesting.