If there is one thing the French never scrimped on, it is markings. Missing those, I'd say the lock and probably the barrel are commercial copies, probably made in what is now Belgium, in the French style. The stock has a very late profile... If I had to guess, I'd say completely commercial product, c.1816-1820. Is there a bayonet lug? It's also quite likely its a cut down commercial musket.
What is now Belgium was an integral part of the French empire from 1794 until 1815. Very few, if any, arms were exported during this period, which coincides with the Quasi-War (1798-1800) and the Napoleonic wars. Needless to say, virtually all Belgian made arms went to the French military and their allies. After the War of 1812, with Belgium now an independent country (which it had never been until then) the export market opened up and we start to see large quantities of arms, especially cheap muskets made on French patterns, exported.
