I agree with Mike Brooks and Rich Pierce. This is not a trade gun, but rather a period restock. With a little imagination, one might call it a frontier restock considering the primitive nature of the work, but that is purely speculative.
Notice that the front finial of the trigger guard has broken off and the guard was inlet that way. Originally, it might have been a simple "acorn" style finial.
The sideplate is missing, but it looks like it was a plain, flat sheet metal held on with screws. There is nothing to suggest that it had a trade gun style sideplate of the dragon/serpent pattern.
Even though the butt plate and trigger guard could be from an 18th century fowling piece, a gun assembled from parts such as this one can be no older than the newest part on it. Based on the shape of the lock mortise, that newest part would be the lock which appears to have been of the type that was commonly available in America in the 1820s and later.
This gun looks like it might have an interesting history, if it could talk, but it's not a trade gun.