The type of action associated with a revolver or autoloader involves the mechanical relationship between the trigger and the hammer, specifically whether or not the trigger will cycle the hammer, or must the hammer be manually cocked. Types of actions include single action, double action (also known as double action/single action), and double action only.
The discussion of action types may seem somewhat convoluted, but after a little exposure to the subject, everybody gets the hang of it.
A single action revolver or a single action autoloader requires that the shooter manually cock the hammer for the first shot. When the trigger is initially pulled, comparatively little effort is required to disengage the hammer and ignite the first round.
With a single action revolver, commonly the frontier or western type, all subsequent shots will require that the hammer be manually cocked. With the single action autoloader, the hammer must be manually cocked for the first shot only. Once the gun is initially fired, the action of the slide automatically extracts and ejects the empty case and cocks the hammer once again. Subsequent shots will require only a light pull on the trigger.
With double action revolvers and double action autoloaders, the initial pull of the trigger cycles the hammer to its full position and then releases it to fire the first shot.
All subsequent shots with a double action revolver will require an extended trigger pull, identical to the first, to cycle the hammer and shoot the remaining rounds. Note that a double action revolver can also be shot in single action mode. This is done by manually cocking the hammer, usually with your thumb, and then pulling the trigger to release the hammer and fire a shot. Trigger pull in the single action mode is lighter than the extended trigger pull of the double action mode. Accuracy may sometimes improve if the shooter has the luxury of time to fire in the single action mode.
Double action autoloaders require a long initial trigger pull to cycle the hammer and fire the first shot in a manner similar to double action revolvers. Because the slide automatically extracts and ejects the spent casing and cocks the hammer, all subsequent shots revert to single action mode, requiring only a slight pull of the trigger.
Like a double action revolver, a double action autoloader may selectively be fired in single action mode for the first shot. This requires the shooter to rack the slide to chamber a round, and then manually cock the hammer. Initial single action mode is only possible on double action autoloaders which feature exposed hammers. First shot trigger pull will be correspondingly light.
A number of manufacturers produce double action only autoloaders. Double action only autoloaders are similar to double action revolvers: relatively heavy trigger pull cocks the weapon and fires the shot.
The double action only design may tend to minimize accidental shootings. Such shootings are thought to be more likely with the light trigger pull of subsequent shots associated with a double action autoloader when it reverts to single action after the initial shot.
An officer of the law may conceivably become involved in a physical struggle with a criminal once a shot has been fired from their duty gun. Inadvertent discharge of the firearm becomes a distinct possibility. To reduce this chance occurrence, some law enforcement agencies and departments are insisting on double action only autoloaders as standard issue.
Choice of the type of action an autoloader should possess is largely a personal matter. Many shooters prefer the single action autoloader. The .45ACP caliber Colt 1911 was the standard issue sidearm for generations of American servicemen. It and its numerous derivatives and clones possess a large following. Military issue now consists of the 9mm Beretta, double action.
To bring a single action autoloader such as the .45ACP caliber Colt 1911, 1911A1 or one of their various derivatives and clones into action in the shortest amount of time requires that it be carried "cocked and locked". This is also known as "Condition 1". A round has been chambered by racking the slide, the hammer has subsequently been cocked by this action, and the safety has been manually engaged.
To deploy the gun, one merely has to release the safety and pull the trigger. Many people are quite comfortable with this method of carry; others find it intimidating. Single action autoloaders may not be the best initial gun choice for the novice shooter. As skills develop with practice, new shooters may wish to further investigate the merits of single action autoloaders.
Double action autoloaders provide the reassurance of a long initial trigger pull for firing the first round and the ease and quickness of firing subsequent rounds associated with single action. In many respects, this combination of features offers the best of both worlds to many shooters.
Care must be exercised at all times, but it becomes especially important after the initial shot is fired from a double action autoloader. Only light pressure on the trigger will cause the firearm to discharge again. Hence, the rules of safety must be engrained in one's behavior to the point where mistakes won't occur. Observance of the top two rules will prevent accidents from happening: watch the direction of the muzzle and keep it pointed in a safe direction; keep your finger off the trigger until you wish to shoot.
foregoing narratives regarding actions of revolvers and autoloaders are
summarized in the following matrix:
Double Action Only
Double Action Only
"Optional" means that shooters may, at their own discretion, choose to manually cock the hammer to take advantage of a shorter, lighter trigger pull. This is only possible on models that feature an exposed hammer. The trigger pull required to cycle the hammer is relatively long and hard for double action only and double action (initial shot only). Note that the terms "soft" and "hard" are relative only in the context of comparing one to the other.