Maka, that is not a Brown Bess lock. Not an American military lock either. It might be a privately purchased English,American,or German lock.
If I found a lock like that I would try to remove some of the rust with oil soaking and a light brushing,by hand with a wire brush. Just enough to see if any maker's mark shows up. A flashlight shining across the face of the lock at a low angle might reveal a mark that could tell its history.