During the farewell scene at the train, the railroad passenger car used as a background is of 20th century design. Passenger cars used in the mid 19th century had metal frames and wooden sides. The car used had obvious steel sides and was probably built around 60 years after the civil war.
The rifles used would produce much more noise and smoke in war. The actors are more than likely using small powder loads and more modern powder. The recoil from firing would also throw the shooter's shoulder back if a full charge had been fired, rather than the small pop and almost no recoil.