An interesting image. You will notice that the buttons are on the wrong side of the coat. This indicates that the photograph has been reversed (mirror image) as would be the case with a tintype. Photographers would attempt to minimize this effect by instructing the soldier to put his leather accouterments on backwards (cartridge box belt over the right shoulder instead of the left). The cap box and bayonet scabbard are likewise worn on the opposite sides. Lastly, the bayonet is turned 180 degrees on the muzzle of the musket (from the right side to the left). So, as this appears to be a Federal private, the "US" on the belt plate, if visible, would also appear reversed.