Factual error: John Blair rides for the pony express, which operated until October, 1861. However, all of the handguns in the movie are cartridge Colts, which did not come into existence until 1871.
Continuity mistake: In this scene we see Buffalo Bill and Wild Bill Hickok in a shootout with the Indians. Hickok has a belt with bullets over his shoulder. The bullets start with nine from the top of the shoulder down, then a space of three then six more bullets. As the gun battle goes on he uses more, then we see a closer shot and now there are fifteen bullets from the top of the shoulder going all the way down the belt.
Factual error: This movie takes place post-civil war, and Fisher, in his first discussion with General Cortinas refers to the "Republic of Texas" being ripe for the taking. Texas ceased to be a republic in 1845, when it joined the United States.