Double Action

Double action (DA) is a trigger mechanism that performs two actions with a single trigger pull – it cocks the hammer and releases it to strike. The shooter does not need to manually cock the hammer before firing, which speeds up the first shot. The trigger pull is longer and heavier than single action.

What is double action

In double action mode, the trigger first rotates the hammer backward against the mainspring through a connecting bar. Once the hammer reaches its rearmost position, the sear releases it to strike the firing pin. The full trigger travel measures roughly 12–15 mm. The force needed to pull the trigger ranges from 4.5–6.5 kg (10–14 lbs). The longer, heavier pull has a side benefit – it acts as a safety feature against accidental discharge.

Double action vs single action

Types of DA mechanisms

DA/SA – the first shot fires in double action mode; the slide then cocks the hammer, and follow-up shots fire in single action mode. Examples: Beretta 92, SIG P226, CZ 75. After the heavier first pull, the shooter continues with a lighter trigger.

DAO (Double Action Only) – every shot fires in double action mode. The hammer returns to its resting position after each shot. Example: Smith & Wesson 642. The pull weight stays the same every time, which simplifies training.

DA with decocker – a DA/SA mechanism fitted with a lever that safely lowers a cocked hammer without firing. Example: HK P30. The shooter can carry the firearm with the hammer down and fire the first shot in DA mode.

Related terms: single action, semi-auto, decocker, DA/SA, DAO