Hi Fernando K,
This is the first time i have seen this type. Most of the time these pistols are double barreled pinfire guns, stamped with the ELG proof mark.
I also don't understand the concept of adding rifling to a blunderbuss barrel, seeing as blunderbusses are mostly used, as far as i understand it, for buckshot and not for a large ball. A large ball would benefit from the spinning effect that the rifling gives it, but buckshot...
Very interesting piece, hopefully someone has some real answers for us.