Trigger Mechanics and Trigger Terminology
Triggers are a complicated business. Aside from being mechanically intricate (and fascinating), a quality trigger can transmit a huge amount of tactile information to an experienced shooter, much the same way good tires can tell a driver about the road they are driving on and what their car is doing at that moment. A variety of terms exist to explain the mechanical and sensory aspects of triggers, some of which are easy to understand, and some not. See below for detailed explanations of the terms that you might hear if you listened in on a discussion of triggers. Don't see what you're looking for, or have something to add? Let us know at guntweaks@gmail.com.
travel, take-up
Travel refers to the distance the trigger must move backward before the firearm fires. Most triggers travel between 1/4" and 1/2", but very specialized triggers may have little or no travel and some older designs can reach toward a full inch.
break
The break is the point in the trigger's travel where the trigger fires the firearm. Triggers intended to provide maximum accuracy should ideally have a break that is sudden and instantaneous; "like snapping a glass rod" is a common comparison. Quality triggers intended for combat often have a slightly "squishier" but still instantaneous break to prevent accidental discharge, sometimes compared to snapping a carrot rather than a glass rod.
pull, weight, pull weight
Trigger weight refers to the resistance that must be overcome by the shooter's finger. Trigger weight is measured using a pull gauge, and in the US that weight is usually expressed in pounds (lb). A 8-9 lb trigger is considered a heavy trigger, a 4-6 lb trigger is common, and a 2-3 lb trigger is considered light. Triggers that measure 1 pound or less are uncommon and can be dangerous for inexperienced shooters to operate.
creep
Creep refers to perceptible travel once the trigger has reached its break point. Ideally, a trigger should have an instantaneous transition from travel to break, but most triggers have some amount of creep, and a perceptive shooter can feel the trigger "ride" the break for a tiny period before the trigger fully breaks. Creep is undesirable and should not be present in high-end triggers, as creep will prevent the shooter from knowing the exact amount of travel and pressure required to fire the weapon.
overtravel
Overtravel is trigger travel after the break. Overtravel is generally undesirable, as it can result in the shooter pulling the gun slightly off course after the break and spoiling the current shot or follow-up shot.
slop
Slop refers to slack, unsupported trigger travel or side-to-side movement. Trigger slop is undesirable and contributes to poor accuracy.
trigger slap
Trigger slap occurs in some auto-loading firearms when the reciprocation of the bolt or slide forcefully resets the trigger to its resting position, "slapping" the shooter's trigger finger back with it along the way. Trigger slap is unpleasant and can sometimes be remedied by polishing the trigger's surfaces, but usually a completely new trigger design is required.
numb
A numb trigger is a trigger that has very few or no tactile indications (sensations) along its travel or before its break. The trigger simply travels and breaks at one weight and feel. Numb triggers have surprise breaks, and are often found on inexpensively manufactured firearms.
surprise break
A surprise break is a break that is not accompanied by an increase in trigger weight. The transition from travel to break is difficult to locate on triggers with surprise breaks, which can be useful in preventing inexperienced shooters from flinching in anticipation of the recoil.
single-stage
A single stage trigger has no substantial difference in pull weight between the travel and break stages.
two-stage
A two-stage trigger has a substantial difference in pull weight between the travel and break stages, with a light, easy travel and a sudden "wall" of resistance prior to the trigger breaking.
single action (SA)
A single action trigger cannot reset the firing pin actuator (hammer, striker) so the firearm will not fire without first being cocked. Because SA triggers do not need to cock the hammer, they are generally lighter and smoother than double action triggers.
double action (DA)
A double action trigger both cocks the hammer (or striker) and actuates the FCG. Because of this, double action triggers usually have heavier pulls and longer travels than SA triggers.
double action/single action (DA/SA)
DA/SA triggers can be lightened by manually cocking the hammer, at which point the trigger travel and weight are reduced to only what is necessary to actuate the FCG (essentially a single action trigger).
double action only (DAO)
DAO triggers cannot be manually cocked, so the trigger pull is only DA and thus is generally heavier and longer than SA or DA/SA (because the trigger both cocks the hammer and actuates the FCG). DAO triggers are more common on duty firearms for law enforcement officers (Glock pistols are a common example), where their long and heavy travel can help reduce the likelihood of an accidental discharge.
Travel refers to the distance the trigger must move backward before the firearm fires. Most triggers travel between 1/4" and 1/2", but very specialized triggers may have little or no travel and some older designs can reach toward a full inch.
break
The break is the point in the trigger's travel where the trigger fires the firearm. Triggers intended to provide maximum accuracy should ideally have a break that is sudden and instantaneous; "like snapping a glass rod" is a common comparison. Quality triggers intended for combat often have a slightly "squishier" but still instantaneous break to prevent accidental discharge, sometimes compared to snapping a carrot rather than a glass rod.
pull, weight, pull weight
Trigger weight refers to the resistance that must be overcome by the shooter's finger. Trigger weight is measured using a pull gauge, and in the US that weight is usually expressed in pounds (lb). A 8-9 lb trigger is considered a heavy trigger, a 4-6 lb trigger is common, and a 2-3 lb trigger is considered light. Triggers that measure 1 pound or less are uncommon and can be dangerous for inexperienced shooters to operate.
creep
Creep refers to perceptible travel once the trigger has reached its break point. Ideally, a trigger should have an instantaneous transition from travel to break, but most triggers have some amount of creep, and a perceptive shooter can feel the trigger "ride" the break for a tiny period before the trigger fully breaks. Creep is undesirable and should not be present in high-end triggers, as creep will prevent the shooter from knowing the exact amount of travel and pressure required to fire the weapon.
overtravel
Overtravel is trigger travel after the break. Overtravel is generally undesirable, as it can result in the shooter pulling the gun slightly off course after the break and spoiling the current shot or follow-up shot.
slop
Slop refers to slack, unsupported trigger travel or side-to-side movement. Trigger slop is undesirable and contributes to poor accuracy.
trigger slap
Trigger slap occurs in some auto-loading firearms when the reciprocation of the bolt or slide forcefully resets the trigger to its resting position, "slapping" the shooter's trigger finger back with it along the way. Trigger slap is unpleasant and can sometimes be remedied by polishing the trigger's surfaces, but usually a completely new trigger design is required.
numb
A numb trigger is a trigger that has very few or no tactile indications (sensations) along its travel or before its break. The trigger simply travels and breaks at one weight and feel. Numb triggers have surprise breaks, and are often found on inexpensively manufactured firearms.
surprise break
A surprise break is a break that is not accompanied by an increase in trigger weight. The transition from travel to break is difficult to locate on triggers with surprise breaks, which can be useful in preventing inexperienced shooters from flinching in anticipation of the recoil.
single-stage
A single stage trigger has no substantial difference in pull weight between the travel and break stages.
two-stage
A two-stage trigger has a substantial difference in pull weight between the travel and break stages, with a light, easy travel and a sudden "wall" of resistance prior to the trigger breaking.
single action (SA)
A single action trigger cannot reset the firing pin actuator (hammer, striker) so the firearm will not fire without first being cocked. Because SA triggers do not need to cock the hammer, they are generally lighter and smoother than double action triggers.
double action (DA)
A double action trigger both cocks the hammer (or striker) and actuates the FCG. Because of this, double action triggers usually have heavier pulls and longer travels than SA triggers.
double action/single action (DA/SA)
DA/SA triggers can be lightened by manually cocking the hammer, at which point the trigger travel and weight are reduced to only what is necessary to actuate the FCG (essentially a single action trigger).
double action only (DAO)
DAO triggers cannot be manually cocked, so the trigger pull is only DA and thus is generally heavier and longer than SA or DA/SA (because the trigger both cocks the hammer and actuates the FCG). DAO triggers are more common on duty firearms for law enforcement officers (Glock pistols are a common example), where their long and heavy travel can help reduce the likelihood of an accidental discharge.
See also: lawyer trigger, match trigger
|
|