1. Single-Action (SA) Trigger
A single-action trigger (or action type) is one of the simplest types of triggers and most long arms (that is, rifles and shotguns) have triggers of this type. A single-action trigger gets that name because the trigger just has one function–it releases the hammer or striker.
This allows the firearm to discharge when the trigger is pulled. However, since this type of trigger performs only a single action or function, with a gun like a typical “Old West” revolver like a Colt Single Action Army revolver or one of the modern clones, you would need to manually cock the hammer before firing each shot.
There are “semi-automatic” single action firearms as well, both rifles, shotguns, and handguns. A semi-automatic just needs the hammer or striker cocked once prior to firing your first shot, and for subsequent shots the reciprocating action of the firearm cocks the hammer or striker automatically, in addition to ejecting a spent cartridge and loading a fresh round.
A single-action trigger is usually lighter and crisper than other types of triggers. One popular example of a SA revolver is a Ruger Blackhawk. Probably the most well-known SA semi-automatic pistol is the Colt 1911 type.
Due to the light, crisp trigger, single-action firearms almost always have a manual safety to help prevent unintentional discharges (or, in the case of the single-action revolver, a large hammer that must be thumb-cocked manually for each shot, as noted above).
2. Double-Action (DA) Trigger
This type of action generally refers to revolvers. With a double-action, pulling the trigger performs two actions: cocking the hammer or striker and firing the firearm. The DA action was popular in “service revolvers” that most police officers carried for the greater part of the 20th century.
A DA revolver has the capability of firing by simply pressing the trigger (though this action is long and relatively heavy), or, the shooter may choose to manually cock the hammer (similar to an SA revolver) and enjoy a short, crisp trigger pull, which is excellent for accuracy.
Dirty Harry’s iconic Smith & Wesson Model 29 chambered in .44 Magnum is one example of a traditional double-action revolver. For The Walking Dead fans, the Colt Python is another iconic DA revolver.
3. Double-Action Only (DAO) Trigger
DAO triggers are popular among defensive handguns–both revolvers and semi-automatics–because they are simple to operate and quick to put into service. As with a traditional double-action revolver, pulling the trigger on a DAO firearm performs two actions: cocking the hammer or striker and firing the firearm. However, unlike a traditional DA, with a DAO you cannot manually cock the hammer because the mechanism is designed only to activate when you pull the trigger.
So, even if you have a semi-automatic handgun with an external hammer, if it is a DAO variant, the hammer will safely return to its fully forward position after each shot, and must be cocked and fired using the long, heavy stroke of the DAO trigger.
oIn addition to the simple function, consistent trigger pull, and lack of any external safety mechanisms to fiddle with, another advantage of a DAO handgun is that it is simpler to cock and fire your next shot than with a single-action revolver. The hammerless Smith & Wesson 640 is a double-action only pistol (technically, it has an internal hammer, but it’s known as a hammerless revolver).
4. Double-Action/Single-Action (DA/SA) Trigger
Typically, the term DA/SA refers to semi-automatic handguns. DA/SA firearms offer the features of both double-action and single-action mechanisms. Like a traditional DA revolver, the DA/SA trigger offers the shooter the option to either press the trigger through a long, heavy stroke for the first shot, or cock the hammer manually for a short, crisp SA trigger break.
There are several potential advantages to a DA/SA pistol and they have been very popular for military and law enforcement use during the last 2 decades of the 20th century. However, be aware that you choose a DA/SA, you will need to master two types of trigger pulls.
If you carry a DA/SA pistol loaded and in safe, hammer-down, “decocked” condition as designed, your first shot will require a long, heavy trigger pull (to cock and fire the hammer or striker), while any subsequent shots will have a shorter, lighter, crisper SA trigger break. This can be difficult for new or unpracticed shooters to deal with.
This transition from DA to SA with each use can affect your accuracy until you become familiar with your firearm. One popular example of a DA/SA semi-automatic firearm is theBeretta 92 series of pistols.
5. Striker-Fired Trigger
Sometimes called “striker-fire” or simply “striker” firearms, this type has no external hammer. The internal striker, or firing pin, is generally partially cocked by the action of chambering a cartridge, and pressing the trigger fully cocks and releases the striker, firing a round.
One advantage to this type of trigger design is that each trigger pull is the same, and there is no external hammer (and often no external safety levers) to snag on clothing. There is also less chance for debris, dirt, mud, etc. to enter the action due to the internal striker design.
Many rifles, shotguns, and handguns are striker-fired designs, but the most well-known is the Glock family of semi-automatic handguns.
Since the Glock has no external safety levers or hammer, it has a safety tab integrated into the trigger that must be pressed in order for the trigger to be pressed fully to the rear to fire the gun.
Firearm Action Types
Now that we’ve covered the primary trigger types, let’s go over the most common firearm actions. They include:
A Note on Semi-Automatic vs. Automatic
A firearm is considered semi-automatic when it fires only one shot each time the trigger is pulled. Semi-automatics can be pistols, rifles, or shotguns. An AR-15 is a semi-automatic rifle, and a Glock is a semi-automatic pistol.
An automatic (or fully automatic, or “full-auto”) weapon continues to fire until its trigger is released, or the ammunition is expended. Automatics are only legal for purchase by civilians in the United States if they were manufactured before May 1986. These firearms are generally not something you can purchase at your typical local gun store, but in many states, you can legally own and shoot fully automatic firearms if you have the proper license.
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