Ask Foghorn: Trigger Terminology

A reader writes:

“trigger’s a bit gritty and prone to stacking” Educate me, please. What is stacking?

One of the major problems with talking about guns is that you’re often trying to convey a feeling with words. Having a common lexicon (standard set of words with known definitions) helps, but only if you’re “in the know.” We went over some of these terms in the first ever Ask Foghorn installment, but today’s Ask Foghorn will try to hit them all. If there’s one I missed (or, more likely, one I got wrong) shoot me an email and I’ll add it to the list or fix it.

Blade

The “blade” of the trigger is the exposed portion to which the shooter applies pressure to fire the gun.

Break

The “break” of a trigger is the point at which the mechanism releases the hammer (or other mechanism that stores potential energy) to hit the firing pin and strike the primer. It is after this point that the firing of the round is out of the shooter’s control — the round is fired and gone, and there’s nothing that can stop it. Well, except the backstop, of course.

The “break” can feel either crisp or soft depending on the shooter’s preference. Crisp triggers are typically preferred on rifles, where the trigger remains stationary until enough pressure has built up for it to release the firing pin. Soft triggers (or “roll triggers”) can sometimes be preferred by competition pistol shooters, which allows the trigger to continue to move backwards while the pressure is building.

Double Action

This term is typically applied to pistols, but it can also be found in other weapons (like the M32 MGL). Unlike a single action trigger, a double action trigger will move the hammer on the firearm backwards, imparting enough potential energy to strike the firing pin and ignite the round, and will also release the hammer once enough energy is stored. This is accomplished in one long, heavy pull to the rear.

Gritty

In contrast to a “smooth” trigger, a “gritty” trigger feels as though the metal trigger is sliding over a rough surface. The force required to pull the trigger may not consistently increase, and will often result in a trigger having properties that are referred to as “stacking.”

Over-Travel

Any rearwards movement of the trigger after the “break” is considered “over-travel.” The further the over-travel, the further the trigger finger must move forward in order to allow the trigger to “reset.” Excessive over-travel and reset distances may fatigue a trigger finger, especially in high round count situations (competition shooting, for example) and lowers the rate of fire for semi-automatic rifles.

Doug wrote in with a quick addition:

In your definition of overtravel, you missed what I feel is probably the most important point about it. The more of it there is, the greater the chance that it will cause the sights to be jerked off target when you come to the end of it.

Reach

The “reach” of a trigger is measured as the distance from the front of the trigger (where your finger would apply pressure) to the front of the grip (behind the trigger). This is essentially a measure of how far forward the trigger is from the grip, which allows you to figure out if your finger is the proper size to manipulate it correctly.

Reset

After the “break,” any further rearward movement of the trigger would be useless. There’s nothing left for the trigger to do — it has performed its function. To make the gun shoot again, once the cycling of the action is complete the trigger must be “reset.” Resetting the trigger is usually no more complicated than allowing it to return to its most forward position, which will re-engage the mechanism to which it is attached. Once re-engaged, the trigger will once again be able to cause a round to be fired. The trigger is usually pushed back into place automatically by an internal spring, and all the operator needs to do is release any pressure on the trigger and cycle the action (if not semi-automatic).

Set

A trigger may sometimes be referred to as a “set” trigger. These triggers give the shooter the option to greatly decrease the force required to pull the trigger past the “break” without breaking out the screwdriver and tearing down the rifle. Sets are usually engaged via a mechanism that is easy to manipulate while the shooter has his sights on a target.

A Single Set trigger means the shooter applies force to the back of the trigger in order to engage the set. This (rather counter-intuitively) moves the trigger further forwards, in the opposite direction that one normally pulls a trigger.

A Double Set trigger requires the shooter to manipulate a lever or catch somewhere on the gun other than the trigger to engage the set.

Within set triggers, there are two types or “phases.” Single Phase set triggers require the set to be engaged before the trigger can be pulled. Double Phase triggers can be fired either with or without engaging the set. Phases are most common on Double Set triggers.

Shoe

A “trigger shoe” is like putting a veneer on your trigger. It’s a piece of material that is affixed to the blade of the trigger in order to make it wider or change some other characteristic of the trigger. Shoes are not typically permanent.

Single Action

A “single action” trigger is one where the only function of the trigger is to release the hammer (or other mechanism that stores potential energy) and enables it to strike the firing pin. That’s it. If the hammer (or mechanism) is already forward and has no potential energy then pulling the trigger will not do anything (unlike a “double action” trigger).  Single action triggers are usually much lighter than double action triggers, and do not move backwards until after the “break.”

Single Stage

See “single stage” in the original Ask Foghorn for more detail, but essentially the trigger does not move until the pressure is sufficient for it to “break.”

Slack

The “slack” is the distance that the trigger moves backwards before resistance is felt. On a two stage trigger it is this slack that comprises the first stage. Slack in a single stage trigger is usually considered a very bad thing. See the original Ask Foghorn for more information.

Smooth

A “smooth” trigger is the opposite of a “gritty” trigger. When pulling a smooth trigger to the rear it will present a constantly increasing level of resistance (or simply constant resistance in a single stage trigger) and will feel like two smooth and oiled pieces of metal sliding across each other. Smooth triggers will not “stack.”

Stacking

A trigger that has “stacking” issues will have an area of unintentionally increased resistance before the “break.” This can also be referred to as a “false break.” In a trigger that has stacking issues the shooter needs to apply enough pressure to get past the “stack,” which is usually enough to move past the “break” as well once the “stack” has been passed. This means that it’s more difficult to control the firearm for precision shots.

Stop

The stop is a physical object (typically a piece of metal machined into the trigger or an adjustable screw) that limits the over-travel of the trigger. The stop will literally stop the trigger from moving any further backwards.

Two Stage

A “two stage” trigger, unlike a single stage trigger, has a bit of “slack” built into the trigger. The shooter takes up the slack in the trigger by applying a small amount of pressure to the trigger. Once the slack is taken up, the trigger is at the “break” location and only needs a small further increase in pressure to fire the weapon. Two stage triggers are useful especially in precision rifles because once the slack is taken up it only requires a very small amount of pressure to fire the gun, less than would be required (or safe) in a single stage trigger.

If you have a topic you want to see covered in a future “Ask Foghorn” segment, email [email protected].