On October 26, 1881, shots rang out at the O.K. Corral. Within the first 30 seconds of the shootout, three members of the Clanton gang were killed. Men on both sides, including Wyatt Earp, Doc Holliday and Billy Clanton, would become legends in part because of what happened in Tombstone, Arizona. They were firing a legendary weapon, too. The Colt Single Action Army held many names over the years. First came its clunky official title, the New Model Army Metallic Cartridge Revolving Pistol. But soon it became known as the Frontier, the Equalizer, the Model P, and most famously,...