Gunsmithing: Install a Better AR-15 Trigger

Gun Digest Gunsmithing with Kevin Muramatsu

The parts you'll need to improve your AR-15 trigger.
The contents of the package splayed about next to the mag well vise block and fire control-less receiver.

As we all know, the AR-15 has become “America’s rifle” in more ways than one. In its latest incarnations, it continues to serve on in our armed forces. As has been shown in this column on more than one occasion, this rifle has spawned an entire host of products to improve performance, ergonomics, or just to make it look cooler.

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Most owners would agree that one aspect of this firearm that needs the most improvement is the fire control system. In other words, folks want a better trigger.

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While the triggers on most factory rifles work, they tend to be heavy, creepy, often gritty, and exhibit a fair amount of take-up and overtravel. The creep, long take-up, and grittiness can be ascribed to the sear engagement; the more sear engagement there is the longer it will take the trigger to “break” (take up), and poorly polished surfaces will cause the grittiness.

Overtravel is the distance the trigger moves backwards after it breaks. Trigger pull weights are almost entirely a function of the hammer spring power, which forces the hammer’s sear engagement surface against the sear. A more powerful spring will increase the trigger pull. A more powerful trigger return spring will also have some effect on the pull weight, but it’s minor compared to the effect from the hammer spring.

Like all the other systems on the gun, there are aftermarket parts — really good ones — to improve your trigger function. In fact, several manufacturers use these triggers as OEM parts in some of their product offerings. A number of two-stage systems are available, including modular units, from Jard, Jewell, Chip McCormick, Geissele, Timney, and from several of the rifle manufacturers. Single-stage trigger units are available from Jard, Chip McCormick, and JP Enterprises. (I’m going to go out on a limb and assume that the reader knows the difference between a single stage and a two-stage trigger).

The setup covered in this column is the unit from JP Enterprises. It’s the single-stage trigger kit I have the most experience with and one that is very, very good. JP offers a kit that includes only the trigger with spring, another that includes and entire fire control package with hammer, springs, disconnector, and anti-walk pins. It also offers a modular fire control unit that drops into the empty hole in a lower receiver with an adjustable selector/safety included.

One reason to write about this package is it’s often installed incorrectly — to be more precise, not correctly enough. The kits come with an extensive instruction sheet and installation CD that are more than adequate for the beginner. But I’m going to replicate this installation more concisely, touching on the “not so correct” points.

Let’s Get Started

Improving the AR-15 trigger: Start with the overset screw.
The first step in the adjustment process. The overtravel screw. Hammer would be cocked for this step but is up for illustration purposes. Note the blood red hammer spring and bright yellow trigger return spring.

Get a magazine well vise block from Brownells and put it in your vise. The first thing to do with the parts is to separate and degrease them thoroughly, particularly the screw threads on the trigger. Clean out your lower, as there’s no sense installing a super-cool trigger and other stuff if you don’t bother to clear the housing of filth.

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Put a small dab of red Loctite on two of the trigger pin screws. Screw these onto one end of each of the trigger/hammer pins. Make sure the pins will fit in your receiver; they’re slightly oversized and may be a very tight fit. (In rare cases, if the pins will not slide in or gently tap in with a plastic mallet, then the holes will have to be reamed.)

You’ll likely have to knock the very top corner tip off the safety engagement surface on the back end of the trigger in order to clear the selector as you push the trigger down into the receiver. Take the trigger, place the trigger return spring on it, and insert it into the receiver.

Here’s where it helps greatly to have two simple tools: Buy two extra firing pins and grind or cut the tips off. These make a perfect “slave pins” for installation and are inexpensive. Use them to retain the trigger and hammer in the receiver during the installation process.

Hammer Springs 101

Important point: Thanks to poor advice given on the internet, it’s become popular to make a lighter trigger pull by reversing the hammer spring on the hammer so it’s installed backwards.

This doesn’t work. Springs are designed to work in one direction. By putting the hammer spring on backward (it’s easily done), the spring force is inconsistent: The hammer will not always fall with enough force to ignite the primer because the spring isn’t building up and releasing the energy it was designed to produce.

The JP kits come with your choice of three different hammer spring strengths. Yellow is three pounds, red is 3.5 pounds, and gray is 4.5 pounds. The yellow is most often used for match or varmint setups, red for match (enhanced reliability) and duty use, and gray for duty and DCM matches.

Whichever one you use, put it on right. See the accompanying illustration for visual perspective.  Next Page →