A revolver is a repeating handgun that has at least one barrel and uses a revolving cylinder containing multiple chambers (each holding a single cartridge) for firing. Because most revolver models hold up to six cartridges, before needing to be reloaded, revolvers are commonly called six shooters or sixguns.[citation needed] Due to their rotating cylinder mechanism, they may also be called wheel guns. Before firing, cocking the revolver's hammer partially rotates the cylinder, indexing one of the cylinder chambers into alignment with the barrel, allowing the bullet to be fired through the bore. The hammer cocking in nearly all revolvers are manually driven and can be cocked either by the user using the thumb to directly pull back the hammer (as in single-action), or via internal linkage relaying the force of the trigger-pull (as in double-action), or both (as in double-action/single-action). By sequentially rotating through each chamber, the revolver allows the user to fire multiple times until having to reload the gun, unlike older single-shot firearms that had to be reloaded after each shot. Some rare revolver models can utilize the blowback of the preceding shot to automatically cock the hammer and index the next chamber, although these self-loading revolvers (known as automatic revolvers, despite technically being semi-automatic) never gained any widespread usage. Although largely surpassed in convenience and ammunition capacity by semi-automatic pistols, revolvers still remain popular as back-up and off-duty handguns among American law enforcement officers and security guards and are still common in the American private sector as defensive, sporting, and hunting firearms. Famous revolver models include the Colt 1851 Navy Revolver, the Webley, the Colt Single Action Army, the Colt Official Police, Smith & Wesson Model 10, the Smith & Wesson Model 29 of Dirty Harry fame, the Nagant M1895, and the Colt Python.
