Tks bob - I was thining if the ctg. shown is correct for the gun, it might be an 8 instead judging by the appearance of length to bullet diameter?

Whatever, it's definitely an interesting piece.

Since I didn't see a rear rolling block ahead of the hammer, I figured a sort of Ballard-type action. The screws or pivot pins on the side of the action appear to be in the wrong possition for a rolling block - but stranger things have definitely happened in large bore gun actions which were custom made - back then - sometimes only a few manufactured or saved for posterity.