Don't confuse history and holleywood.
Both words start with an H and that is all there is in common. There were no authenticity consultants when that movie was made. Many of the old Civil War movies were shot using post CW 45-70 Trapdoor Springfields. If they had bolt action 03 Springfield’s or Remington rolling block rifles or M-16s in the studio's inventory they would have used them also.