Factual error: When the "U.S." soldiers open fire on the Mexican cavalry, they employ a machine gun. The only two rapid-firing weapons in that time period were the Gatling gun, which used a magazine or drum of rounds and was fired by turning a crank, or the "Mitrailleuse" volley gun, which required at least two men to operate it, one to load the ammunition blocks, and the other to turn, once again, a crank to fire the weapon. The gun pictured has a single operator and neither a crank, nor any visible cartridge feed.
Factual error: The mitrailleuse (weapon)the bandits, who are disguised as US troops, use to gun down the Mexican soldiers is shown to have 46 barrels, yet shoots far more bullets than it can hold. Additionally, reloading is a very lengthy process.