Sear (firearm)

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In a firearms, the sear is a sliding surface, usually a tooth on a lever on the trigger, sliding against a tooth on the firing pin or hammer. A pre-determined amount of leverage on the trigger will pull down the horizontal, forward pointing lever part of the trigger inside the gun. This will slide down a small upward pointing tooth on the lever from the corresponding tooth on the striker or hammer. This frees it to strike the firing pin, which then strikes the rear cartridge case, allowing the firearm to discharge.

Sears are also used elsewhere in the fire control group of certain firearms, and occasionally the firing mechanism is simplified to integrate the trigger and sear as one part. For instance, in the M16 rifle, the single-piece trigger directly engages the hammer. Likewise, also in the M-16, the 'auto sear' is responsible for engaging the hammer in a separate groove than the trigger so as to delay the hammer's release until the bolt assembly is in battery and ready to fire the next round. Without the auto sear, the hammer would follow the bolt forward through the receiver and not deliver the proper blow to the rear of the firing pin, making automatic fire a statistical exception rather than a rule.

The term 'sear' is sometimes (incorrectly) used to describe a complete trigger group.

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