Definition of "Single Action"in Firearms Terminology

Traditions single action 45 revolver
Photo of a Traditions single action 45 revolver. Photo © Russ Chastain

Definition

Single action (SA) refers to any firearm that must be manually cocked before each shot. In such guns, the trigger performs a single function (releasing the hammer to fire the gun), thus the "single" in the name. Single action most often applies to handguns, but may also refer to long guns (rifles and shotguns) as well. The SA trigger is historically the oldest and simplest type of trigger mechanism.

The term "single action" was not used until the introduction of double action guns in the mid-19th century, in which pulling the trigger both cocked the hammer and released it to shoot the firearm.

Most firearms of single-action design are revolvers, but some semi-automatic pistols fit the bill, such as the Colt 1911, which must be manually cocked before the first shot may be fired, and is then automatically cocked for successive shots. Such pistols are sometimes referred to as SAO, meaning "single action only."

Some semi-auto pistols are DA/SA (double action/single action), meaning that the first shot may be fired without manually cocking the hammer in a separate operation (double action), and each successive shot is then fired single action, because the automatic operation of the pistol, (induced by the firing of a cartridge), cocks the gun to ready it for the next shot.