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Single Action
Single action (SA) is a trigger mechanism where the trigger performs only one job – releasing the cocked hammer. The hammer must be cocked by other means: manually with the thumb (on revolvers) or by the slide movement (on semi-automatic pistols). The result is a short, light trigger pull.
What is single action
In single action mode, the trigger simply releases the sear that holds the cocked hammer. The hammer, driven by spring tension, strikes the firing pin. Trigger travel measures roughly 3–6 mm, and pull weight falls between 2–5.5 lbs. On a Colt SAA revolver, factory pull weight sits around 3.5–5.5 lbs; on a 1911 pistol, it is approximately 4 lbs. The short travel and low pull weight allow more accurate shooting because the hand moves less during the trigger press.
Single action vs double action
| Feature | Single action (SA) | Double action (DA) |
|---|---|---|
| Pull weight | 2–5.5 lbs | 10–14 lbs |
| Trigger travel | 3–6 mm | 12–15 mm |
| Accuracy | Higher (light, short pull) | Lower (heavier pull disturbs aim) |
| First-shot speed | Slower (hammer must be cocked) | Faster (no cocking needed) |
| Safety | Requires a manual safety | Heavy pull guards against accidental discharge |
Types of SA firearms
SA revolvers – the shooter must thumb-cock the hammer before each shot. The classic example is the Colt Single Action Army (SAA). This design dates back to the 19th century and is still found in Western-style replicas today.
SA semi-automatic pistols – the slide movement cocks the hammer during the cycling process. The shooter manually cocks the hammer only before the first shot; after that, the slide cocks it automatically. Example: Colt 1911.
DA/SA pistols in SA mode – pistols with a switchable mechanism (e.g., CZ Shadow 2) operate in SA mode after the first shot or after the shooter manually cocks the hammer. This gives a lighter pull for more precise follow-up shots.
Related terms: double action, DA/SA, semi-auto, hammer, trigger mechanism