I bought this. It's a 1777 AN IX "corrected", the model commissioned by Napoleon Bonaparte in 1799/1800. It post dates the American Revolution. This is an untouched original made at the Mutzig arsenal and is a really nice piece (Mutzig is one of the 5 state arsenals approved for manufacture by Napoleon after consolidation). Had a French gentleman school me pretty well on this piece. It is most certainly a Charleville musket that armed the French army, likely seeing action in the European battles of the early 1800s.
It's certainly NOT a fowling shotgun