Factual error: When McNelly dictates his last will and testament, he leaves, among other items, his Navy Colts to Dunnison. He may well have a couple of Navies stashed in his belongings somewhere, but the pistols he wore and used were .44 peacemakers.
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.