I took note of the weapon he is holding also, which appears to be a flintlock, 1816 Harpers Ferry, .69 caliber. Also look at this picture closely and it seems to be a "reverse" or mirror image of what the eye would have seen. Since the lock mechanisms on those muskets were always on the right side, he appears to be holding the left side of the weapon to the front, then actually his RIGHT hand is on the forearm and his LEFT is on the grip behind the trigger guard.
Seems we have discussed another reverse picture like this once before if my memory serves me correct.