Double-Action (DA)/Single-Action (SA)
Double-Action (DA)
The double-action (DA) revolver uses a long pull of the trigger to cock the hammer, rotate the cylinder and fire the piece. Repeated shots may be fired by repeatedly pulling the trigger until all rounds have been fired. Many DA revolvers may be thumb-cocked and fired in single-action mode as well, while others have enclosed hammers and may be fired only in double-action mode.
Double-action firearms have a longer, stiffer trigger pull than a single-action gun because you’re doing the extra work of cocking the hammer with the trigger.
Single-Action (SA)
A single-action (SA) trigger is the earliest and mechanically simplest of trigger types. Single-action means pulling the trigger does one action: It releases the hammer or the striker. With a single-action pistol, if the gun’s not cocked, pulling the trigger actually does nothing. You have to manually pull the hammer back, and then pulling the trigger will release it. Cocking the hammer rotates the cylinder. This action brings a new round into alignment with the barrel. Once cocked, the SA revolver trigger must be pressed to fire. The hammer must be re-cocked to fire another round. A single-action pistol will have a shorter, lighter trigger pull than a double-action because the hard part — pulling back the hammer — is already done.
The term SA was not used until the introduction of double-action revolvers in the mid-19th century. Prior to that, all triggers were SA (matchlocks, flintlocks, percussion rifles, etc.)
Double-Action/Single-Action (DA/SA)
A double-action/single-action (DA/SA) firearm combines the features of both double- and single-action mechanisms. When the firearm discharges, the cycling slide will automatically cock the hammer to the rear. The rest of the shots fired will be in single-action mode, unless the hammer is manually lowered again. This action is also known as traditional double-action (TDA).
DA/SA typically refers to a semi-automatic, but in the case of a revolver, double-action generally means a weapon combining the ability to fire both double- and single-action. The trigger mechanism function of a DA/SA semi-automatic handgun is identical to a DA revolver. However, this is combined with the ability of most semi-automatics to self-cock the hammer when firing. The pistol can be carried with the hammer down on a loaded chamber, unlike a single-action semi-automatic. When the user is ready to fire, simply pulling the trigger, in double-action mode, will cock and release the hammer. This gives the positive aspects of a single-action trigger without the need to carry “cocked and locked” (with a loaded chamber and cocked hammer), or with an empty chamber, which requires the user to chamber a round before firing.
Double-Action (DA) or Double-Action Only (DAO)
A double-action, also known as double-action only (DAO), is a design which either has no internal mechanism capable of holding the hammer or striker in the cocked position (semi-automatics), or has the entire hammer shrouded and/or has the thumb spur machined off, preventing the user from cocking it (revolvers).
This design requires a trigger pull to both cock and trip the hammer/striker for every single shot, unlike a DA/SA, which only requires a double-action trigger pull for the first shot (or a typical DA/SA revolver, which can fire single-action, but uses double-action as a default). There is no single-action function for any shot. The hammer or striker always rests in the down position until the trigger pull begins. With semi-automatics (unlike DA/SA weapons) the hammer does not remain cocked after the first round is fired. Every shot is in double-action mode. When it comes to a revolver, the shooter does not have the option of cocking the gun before shooting and must always discharge it in double-action mode.
Related Articles From the USCCA Blog
Double-Action Carry Guns: Make Training Fit Reality
John Caile — August 2, 2019
Single-Action Auto: “Cocked and Locked” Carry
Scott W. Wagner — December 22, 2017
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