When Orry is fighting Justin, the scar on Justin's face changes from the left side to the right side in different shots.
Before Bent leads the blindfolded Ashton upstairs to the room full of goodies, his suit changes between the time they leave the carriage and when they enter the house.
When Augusta takes care of Charles' injury, she puts his shirt around his shoulders. In the next shot, the shirt is gone and then immediately after that is back around his shoulders.
Not only are Berdan's Sharpshooters incorrectly shown to be at the First Battle of Bull Run, but they are shown in that and subsequent battles as fighting as part of the Union line. In actuality, the sharpshooters fought as skirmishers, ahead of the line, targeting confederate officers and other selected targets, in small groups. As the enemy advanced these skirmishers would melt back behind the main line units and continue sniping while the regulars engaged with volley fire.
When the buggy loses a wheel and Brett steps into the creek, the hem of her dress is already wet from a previous take.