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How A Single Action Semiautomatic Handgun Functions

How A Single Action Semiautomatic Handgun Functions

1911 Function

How A Single Action Semiautomatic Handgun Functions



A single-action (SA) trigger is the earliest and mechanically simplest of trigger types. It is called the “single-action” because it performs the single action of releasing the hammer or striker to discharge the firearm each time the trigger is pulled, while the hammer must be cocked by separate means.  Almost all rifles and shotguns use this type of trigger (with certain exceptions, such as the Armsel Striker and certain law-enforcement Mossberg 590DA1 shotguns).

The term “single-action” wasn’t in use until firearms with double-action triggers were invented, which didn’t occur until the mid-19th century; before that, all triggers were single-action (for example, all matchlocks, flintlocks, muskets, etc.). While originally all hammers required a separate hand motion to cock manually, with the birth of repeating rifles such as the Henry rifle, it was found to be easy to design the cocking of the hammer into the cycling of the action, which is still found in most modern repeating firearms, and some single-shots as well. Although these firearms don’t require the user to physically cock the hammer, they are still single-actions because the cocking is not performed by the trigger mechanism. Manually-cocked triggers lasted much longer on revolvers; due to the limited size and weight of handguns, it was difficult to fit the necessary mechanisms in place, and most repeating rifles required the use of two hands to cycle the action. Thus the “classic” single-action revolver of the mid-to-late 19th century includes black-powder percussion-cap muzzleloaders such as the Colt 1860 “Army” Model, and Colt 1851 “Navy” Model, and European models like the LeMat, as well as early metallic-cartridge black-powder revolvers such as the Colt Model 1873 “Single Action Army” (named for its trigger mechanism) and Smith & Wesson Model 3, all of which required a thumb to cock the hammer before firing. Manually cocked hammers lasted a while longer in some break-action shotguns, and in dangerous game rifles, where the hunter didn’t want to rely on an unnecessarily complex or fragile firearm. While single-action revolvers never lost favor in the US right up until the birth of the semi-automatic pistol, double action revolvers, such as the Beaumont–Adams, were designed in Europe before the American Civil War broke out, and saw great popularity all through the latter half of the 19th century, with certain numbers being sold in the US as well.

In modern usage, the terms “single-action” and “double-action” almost always refer to handguns, as very few if any rifles or shotguns feature double-action triggers. While a “single-action” revolver or semi-automatic must always be cocked prior to firing (either manually or by the operation of the firearm), most “double-action” handguns are capable of firing in both single- and double-action modes. Only “double-action only” firearms are incapable of firing from a cocked hammer. It is a common misapprehension that “double action” refers to the ability to fire in both modes, but as stated above, the term stems from the number of actions performed by the trigger when pulled, not the operating modes it is capable of using.

While many European and some American revolvers were designed as double-action models throughout the late 19th century, for the first half of the 20th century, all semi-automatics were single-action firearms, requiring the firearm to be carried cocked with the safety on, or with an empty chamber (Colt M1911, Mauser C96, Luger P.08, Tokarev TT, Browning Hi-Power). The difference between these firearms and single-action revolvers is that while a single-action revolver requires the user to manually cock the hammer before firing, a single-action semi-automatic is automatically cocked when the user cycles the slide to chamber a round. Thereafter, every time a round is fired, the hammer is recocked by the cycling slide and is thus always cocked unless the user manually lowers the hammer, or pulls the trigger on an empty chamber (firearms lacking automatic-hold-open feature only).

In the late 1930s and early 1940s, Walther introduced the first “double-action” semi-automatics, the PPK and P.38 models, which featured a revolver-style “double-action” trigger, which allowed the firearm to be carried with a round chambered and the hammer lowered. After the first shot, they would fire as single-actions. These double action, or “double action/single action”, pistols rapidly gained popularity, and the traditional single-action rapidly lost favor, although they still retain a dedicated following. Today, a “typical” revolver is a “double-action”, which can be fired in single action when wished, and the most common form of a semi-automatic is the “DA/SA”, carried in double-action mode but firing most of its shots in single-action mode.

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Eric Beer | BC Firearm Academy

3229 Fraser St, Vancouver, BC V5V 4B8


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