Trigger (firearms)

A trigger is a mechanism that actuates the function of a ranged weapon such as a firearm, airgun, crossbow, or speargun.

The word may also be used to describe a switch that initiates the operation of other non-shooting devices such as a trap, a power tool, or a quick release.

This is accomplished by actuating a striking device through a combination of mainspring (which stores elastic energy), a trap mechanism that can hold the spring under tension, an intermediate mechanism to transmit the kinetic energy from the spring releasing, and a firing pin to eventually strike and ignite the primer.

A striker is essentially a firing pin directly loaded to a spring, eliminating the need to be struck by a separate hammer.

Variable mechanisms will have this surface directly on the trigger and hammer or have separate sears or other connecting parts.

The break is often considered the most critical stage of the trigger pull for achieving good practical accuracy, since it happens just prior to the shot being discharged and can cause some unwanted shakes from the shooter's hand at the instant of firing.

A perceivably slow trigger break is often referred to as a "creep", and frequently described as an unfavorable feature.

It can be a very critical factor for accuracy because shaking movements during this phase may precede the projectile leaving the barrel and is especially important with firearms with long barrels, slow projectiles and heavy trigger weights, where the more significant resistance drop can make the trigger finger overshoot and shake in an uncontrolled fashion.

Having some overtravel provides a "buffer zone" that prevents the shooter from "jerking the trigger", allowing the remnant pressing force from the finger to be dampened via a "follow-through" motion.

Although a perceivable overtravel can be felt as adding to the "creep" of the trigger break, it is not always considered a bad thing by some shooters.

Single-action triggers with manually cocked external hammers lasted a while longer in some break-action shotguns and in dangerous game rifles, where the hunter did not want to rely on an unnecessarily complex or fragile weapon.

While many European and some American revolvers were designed as double-action models throughout the late 19th century, for the first half of the 20th century, all semi-automatic pistols were single-action weapons, requiring the weapon to be carried cocked and loaded with the safety on, or uncocked with an empty chamber (Colt M1911, Mauser C96, Luger P.08, Tokarev TT, Browning Hi-Power).

The difference between these weapons and single-action revolvers is that while a single-action revolver requires the user to manually cock the hammer before each firing, a single-action semi-automatic pistol only requires manual cocking for the first shot, after which the slide will reciprocate under recoil to automatically recock the hammer for a next shot, and is thus always cocked and ready unless the user manually decocks the hammer, encounters a misfiring cartridge, or pulls the trigger on an empty chamber (for older weapons lacking "last round bolt hold open" feature).

Such trigger design either has no internal sear mechanism capable of holding the hammer/striker in a still position (so cocking and releasing have to happen in one uninterrupted sequence), or has the whole hammer shrouded and/or with the thumb spur machined off, preventing the user from manipulating it separately.

This design requires a trigger pull to both cock and trip the hammer/striker for every single shot, unlike a DA/SA, which only requires a double-action trigger pull for the first shot (or a typical DA/SA revolver, which can fire single action any time the user wishes but uses double-action as a default).

This means that there is no single-action function for any shot, and the hammer or striker always rests in the down position until the trigger pull begins.

With semi-automatics, this means that unlike DA/SA weapons, the hammer does not remain cocked after the first round is fired, and every shot is in double-action mode.

Although there have been revolvers that were designed with trigger mechanisms totally lacking a single-action mechanism altogether,[2] more commonly DAO revolvers are modifications of existing DA/SA models, with identical internals, only with access to the hammer prevented, either by covering it with a shroud or by removing the thumb spur.

For striker-fired pistols such as the Taurus 24/7, the striker will remain in the rest position through the entire reloading cycle.

However, in practice most double-action guns feature the optional ability to cock the hammer separately, reducing the trigger to perform just one action.

When the user is ready to fire, simply pulling the trigger will cock and release the hammer in double action mode.

The latter is the more popular because, without a decocker, the user is forced to lower the hammer by hand onto a loaded chamber, with all of the attendant safety risks that involves, to return the gun to double-action mode.

There are some revolvers that can only be fired in double-action mode (DAO), but that is almost always due to existing double-action/single-action models being modified so that the hammer cannot be cocked manually, rather than from weapons designed that way from the factory.

Examples include the AR-15 series of rifles, produced by Franklin Armory, Fostech Outdoors, and Liberty Gun Works.

The Taurus PT 24/7 Pro pistol (not to be confused with the first-generation 24/7 which was a traditional pre-set) offered this feature starting in 2006.

On a single-action revolver, for which the hammer must be manually cocked prior to firing, an added level of safety is present.

On a semi-automatic, the hammer will be cocked and made ready to fire by the process of chambering a round, and as a result an external safety is sometimes employed.

The primary drawback is that the additional trigger pull weight and travel required for each shot reduces accuracy.

Glock popularized this trigger in modern pistols[citation needed] and many other manufacturers have released pre-set striker products of their own.

In normal handling of the firearm, this is not an issue; loading the gun requires that the slide be retracted, pre-setting the striker.