Pistols today – both semi-automatic and revolvers – are manufactured in several different actions, which refers to the function of its trigger, hammer and safety. Among the most common pistol actions include single-action and double-actions. So, what's the difference between these two actions and which one comes out on top as the winner?
With a single-action pistol, pulling the trigger drops the hammer, which in turn fires the chambered round. Because there's only one action taking place with the trigger pull – dropping the hammer – they are referred to as “single-action.”
The main benefit offered by this action is a lighter trigger pull, often requiring just 4-5 pounds of pressure. However, single-action revolvers must be manually cocked before each shot, which takes both time and energy. With some newer single-action semi-automatic pistols, only the first round must be cocked, at which point each subsequent shot will automatically cock the hammer back (see SA/DA below).
While single-action pistols only drop the hammer, double-action pistols both cock back and release the hammer (or striker) when the trigger is pulled. Because there are two steps in double-action pistols, they tend to have a heavier, longer trigger pull when compared to their single-action counterpart.
Keep in mind that double-action pistols cannot be manually cocked back. This may deter some people from using them, as firing a shot requires more time and effort. On the other hand, the longer trigger pull can reduce the risk of an accidental discharge, which is particularly beneficial for people who carry a loaded pistol.
A third option is a double-action/single-action (DA/SA), which lives up to its namesake by combining the characteristics of both actions. Also known as traditional double-action, they function similar to a double-action, although the hammer is typically cocked back when the slide is recoiled (for semi-auto pistols). When you initially pull the slide back to move a round from the magazine into the chamber, a DA/SA semi-automatic pistol will also cock the hammer back. This means your first shot is a single-action, as pulling the trigger only drops the hammer, but each subsequent shot will function as a double-action.
A neat feature that's often included in DA/SA semi-automatic pistols is a decocker. This feature allows the user to safely drop the hammer without engaging the firing pin. If you want to carry a loaded DA/SA pistol without the hammer back, you can pull back the slide and then use the decocker to safely drop the hammer. Most decockers work by blocking the hammer or covering the firing pin, preventing the gun from firing.
Video: Single Action Vs. Double Action Firearms: