I really fancy that selector on the top tang. It looks to be post 1912 & pre-1923. It is some unique Blitz action with a pretty big bore. Is the word "Nitro" on either side of the scattergun tubes? You are probably going to have to make a chamber cast or make a best guess at cartridge length. Ford can tell you what parent case from which to form the brass.

Kind Regards,

Raimey
rse