This is a U.S. marked Colt .45 caliber Single Action Army revolver, Model 1873, manufactured in 1878. It has proper markings and inspectors' cartouches on the grips.

This is the type of revolver was issued to troops during the late 1800s Indian Wars, including to the unfortunate mounted soldiers under Gen. George Custer's command in The Battle of Little Big Horn. This sidearm was used along with the M1873 Springfield Trapdoor single-shot carbine.