Check if it has a patent vent in the inner aspect of the pan.
Does the hammer's screw move a if you try to unscrew it, or is it fixed/soldered?
Normally, the end of Hammer screws in the 18th C were pointy, if it is flat, it's a bad sign.
Usually, there are screws that go through the outer face of the lock, and engage the plate on the opposite side. The screw positions in yours do not seem to correspond in this manner.
Does it have any poincons, words, signs inscribed on the barrel?
There were fake guns made for decoration purposes during Victorian times, these had a very weak action spring, and couldn't fire. The wood work was rather elaborate.
If I were you, I would disarm the lock and check if the inner workings correspond to the Real McCoy.
G'luck!
M
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