colt single action army
A six-shot single-action revolver, developed by Colt's Patent Fire Arms Manufacturing Company starting in 1869, adopted (in its .45 Colt chambering) as the official sidearm of the United States Army in 1872, and mass-produced starting in 1873.
The military version was called the Single Action Army, Model 1873, for reasons that should be obvious; its proper civilian product name when first introduced was "New Model Army Metallic Cartridge Revolving Pistol", which, astonishingly, failed to catch on. Common nicknames include "Peacemaker" and "The Gun That Won the West".