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The trigger is one of the most critical parts of the gun that you interact with, enabling you to fire the weapon at will. While many trigger mechanisms share the same basic parts and operating principles, they can also differ in some important ways.
The trigger is the part that you press to discharge a firearm. The act of manipulating the trigger to fire the weapon without disturbing the sight picture is called “trigger control,” which is an essential component of marksmanship.
Although it’s common to see references to trigger pull, trigger control requires that you squeeze the trigger by applying gradual, continuous rearward pressure until the trigger breaks.
There are a wide variety of trigger mechanisms in small arms, depending on the purpose for which it was designed and how the hammer/striker is released. For example, in rifles designed for precision and competitive target shooting, a lightweight break and short reset are preferred. In military rifles, the trigger mechanism tends to be relatively heavy, which, unfortunately, can discourage good shooting habits.
Several elements comprise the sequence of trigger operation. These are:
Take-up, also called slack, is any movement between the trigger’s resting position and the point at which it meets the sear/mainspring resistance.
When you take up the slack, you squeeze the trigger through its free movement until you hit the wall. This is the point at which the trigger causes sear movement. You should expect to feel additional resistance from the hammer spring/mainspring.
Creep is any trigger movement that causes sear/hammer movement. If you can feel the trigger stopping and starting as it moves the sear or hammer, there is pronounced and inconsistent creep. The priority of gunsmiths and manufacturers is typically to reduce creep in single-action trigger mechanisms. However, in double-action trigger mechanisms, this is less practical.
Also called trigger release, trigger break refers to the point at which the trigger mechanism releases the hammer or striker, firing the cartridge. If there’s a live cartridge in the chamber, you’ll hear a gunshot.
If the chamber’s empty, you’ll hear a click as the hammer hits the bolt and firing pin. A related concept is lock time, which is the time interval from trigger break to primer ignition. This time interval is usually a few milliseconds.
Over-travel is the distance the trigger is capable of moving following trigger break/release. Any device that limits over-travel is called a trigger stop. In some weapons, over-travel is adjustable using a screw. If the over-travel screw is not used, the trigger will typically stop when it hits the frame.
After you’ve pressed the trigger and fired the weapon, you need to relieve pressure from the trigger in semi-automatic firearms to allow it to reset. Trigger reset prepares the firing mechanism for a subsequent trigger press. In competitive shooting sports, a short, fast reset can enable you to fire the weapon more rapidly, as the trigger doesn’t have to move as far forward after it breaks.
AR-15 Trigger Mechanisms
Before discussing what makes an AR-15 trigger assembly good, it’s important to discuss how the fire-control group functions.
Retracting the charging handle cocks the hammer. When the hammer is cocked, you can rotate the selector lever to the “Safe” position. On “Safe,” the selector, which is cylindrical inside the lower receiver, prevents the trigger from pivoting. When set to “Fire,” the selector exposes a recess, which permits the rear of the trigger to move upward.
The hammer has a hook that catches on the front of the trigger when cocked. As you press the trigger, it pivots about the trigger pin, lowering the front of the trigger and releasing the hammer.
The hammer spring is now free to drive the hammer forward. The hammer impacts the rear of the firing pin on its forward stroke, driving it through the bolt face and into the cartridge primer. This fires the cartridge and initiates the reloading cycle.
As the bolt carrier group cycles, it forces the hammer down, at which point the disconnector catches the hammer. When you release the trigger, the front of the trigger engages the hammer and the disconnector lifts out of engagement.
Attributes of a Good Trigger
The elements that contribute to a good AR-15 trigger assembly begin with a crisp break. The break, as noted, is when the trigger releases the hammer or striker, firing the weapon.
A break can be long, heavy, and creepy. On the other hand, a crisp break is one in which there is little to no perceptible movement of the trigger between hitting the wall — meeting sear resistance — and releasing the hammer. This is often likened to breaking a glass rod — there are no sudden stops and starts during sear engagement and trigger break. You may not perceive any movement of the trigger at all following take-up.
Roughness and Smoothness
Another factor that affects the trigger pull is roughness. This is sometimes called “grit.” If the engagement surfaces between the trigger, hammer, and disconnector are not ground smooth by the manufacturer, this can cause inconsistent or unpredictable trigger creep.
Some manufacturers choose to use special coatings or platings to reduce friction between these surfaces and increase lubricity. The result is a considerably smoother trigger action, which distracts you less as you press the trigger.
While minimizing creep in single-action firearms tends to be a priority, you shouldn’t discount the importance of smoothness. It’s also essential to avoid noticeable “stacking,” where trigger resistance steadily or suddenly increases during the creep part of the sequence. Consistency of trigger operation is critical.
The weight of the trigger is more complex. Mil-spec triggers tend to be heavy. While a heavy trigger is not necessarily an impediment to accurate shooting, there is a point at which increasing the weight increases discomfort or causes strain. A trigger that is too light and sensitive to any pressure or vibration can be a liability, discharging due to impact.
There are multiple overlapping functions here that lend themselves to refinement. In the past, if you purchased an ArmaLite-pattern rifle, you were limited to the mil-spec trigger mechanism installed at the factory. If you wanted to improve the trigger mechanism, you would either have to elicit the services of a gunsmith or attempt it yourself.
Since the expiration of the federal assault weapons ban in 2004, the market for spare and replacement parts, accessories, and other equipment related to the AR-15 platform has exploded. Now you have a variety of drop-in trigger assemblies that you can buy and install in minutes.
In the four rules of firearms safety, Rule #3 reads: “Keep your finger off the trigger until your sights are on the target.” Adherence to this rule is referred to as trigger discipline. This consists of keeping your index finger straight alongside the frame or receiver until your sights are on target or the muzzle is pointed toward a specific threat.
Any number of stress-induced physical reactions can cause you to inadvertently press the trigger, which is why it’s essential to practice trigger discipline even when attempting to take an intruder at gunpoint.
The Bottom Line
The standard mil-spec AR-15 trigger assembly may be sufficient for most purposes, but there is room for improvement. Once you understand what makes a good trigger, you can search for a suitable drop-in replacement.