I've been shooting , and repairing Black powder rifles and shotguns since 1977, and can tell by the nose cap, trigger guard, hammers, hooked breech, and checkering, that this is not a hardware store gun but a decently made English fowler.if you remove the lock you will likely see a little metal piece behind the bridal ( something that looks like a snail ) , the little metal piece is called a" fly" or detente, that prevents the sear from hitting the half noodle notch on the tumbler when it is fired.
The cheaper guns, as well as the other things i mentioned, never had this.
If you look at the underside of the barrels as well, you may see a note that says "not for ball" or choke"
If it was a cheaper hardware gun proofed in England but made with parts from Continental Europe, it would have the crown and mace proofs but would also have a note saying "not English made"
Hope this helps.
Ge the barrel checked out and if it's okay, feel free to contact me and can walk you through the whole process of shooting that fine piece.
Cat