Double action is a firearm operating system where a single pull of the trigger performs two distinct functions: it both cocks the hammer (or striker) and then releases it to fire the weapon.
This mechanism simplifies the firing process as there's no need to manually cock the hammer before the first shot, distinguishing it from single-action systems.
Understanding Double Action Operation
In firearms equipped with a double-action system, the trigger pull is typically longer and heavier compared to a single-action system. This longer pull provides a safety mechanism, making accidental discharges less likely.
The two main functionalities performed by a single trigger pull in a double-action firearm are:
- Cocking the Hammer: The initial part of the trigger pull rotates the hammer backward, setting it into a ready-to-fire position.
- Releasing the Hammer: As the trigger pull continues, it reaches a point where it releases the hammer, allowing it to strike the firing pin and ignite the primer, thus firing the cartridge.
Double Action vs. Double-Action Only (DAO)
While the term "double action" broadly describes the trigger's ability to cock and release the hammer, there's a specific variant known as Double-Action Only (DAO).
| Feature | Double Action (DA/SA) | Double-Action Only (DAO) |
|---|---|---|
| First Shot | Can be fired in double-action mode (long, heavy pull). | Always fired in double-action mode (long, heavy pull). |
| Subsequent Shots | Can be fired in single-action mode (shorter, lighter pull) if the hammer remains cocked. | Always fired in double-action mode, as the hammer decocks after each shot or is always reset by the trigger. |
| Hammer State | Can be manually decocked or left cocked. | Hammer generally rests forward (decocked) and must be fully cocked by the trigger pull for every shot. |
| Primary Use | Many traditional revolvers and some semi-automatic pistols. | Often found in concealed carry firearms where simplicity and consistent trigger pull are desired. |
In a Double Action/Single Action (DA/SA) firearm, the first shot can be fired in double-action mode. After the first shot, or if the hammer is manually cocked, subsequent shots can be fired in single-action mode, which typically involves a much lighter and shorter trigger pull.
Double-Action Only (DAO) firearms, however, always operate in the double-action mode. Every shot, including the first, requires the trigger to both cock and release the hammer. This results in a consistent, heavier trigger pull for every shot, which can be beneficial for training and safety, as there's no change in pull weight between shots.
Practical Implications
The choice between double-action, single-action, or double-action only systems impacts a firearm's handling characteristics, particularly for self-defense or competitive shooting.
- Safety: The longer and heavier pull of double-action triggers provides a greater margin of safety against accidental discharge, especially when carrying a loaded firearm.
- Consistency: DAO systems offer a consistent trigger pull, which can be advantageous for muscle memory and training.
- First Shot Capability: Double-action allows for immediate firing without manually manipulating the hammer, making it ideal for scenarios requiring quick deployment.
For more in-depth information, you can explore resources on firearm operating systems.
