Topic summary
Single-action
Extracted from the Wikipedia article Trigger (firearms).
Single-action
A single-action (SA) trigger is the earliest and mechanically simplest of trigger types. It is called "single-action" because it performs the single function of releasing the hammer/striker (and nothing else), while the hammer/striker must be cocked by separate means. Almost all single-shot and repeatinglong arms (rifles, shotguns, submachine guns, machine guns, etc.) use this type of trigger.