Gunsmithing: Install a Better AR-15 Trigger – Part 2

Gun Digest Gunsmithing with Kevin Muramatsu
Adjust, Adjust, Adjust

Once the trigger and hammer are installed, you can add the overtravel adjustment screw. Cock the hammer. Take the shorter of the two small headless screws, dab a bit of red Loctite on it (don’t skimp, you can always wipe off the excess), and screw it in all the way.

Place your least favorite thumb in front of the hammer to prevent the hammer from hitting the receiver. Then hold the trigger back and unscrew the screw until the hammer falls. Do this a couple of times and then go just a teeny bit farther. There should be just the tiniest bit of trigger jiggle, with no interference with the hammer once the trigger is pulled.

If you’re holding the trigger back and you hear a slight scraping noise when you rotate the hammer, you don’t have enough overtravel.

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Uncrew it a tiny bit more until the scraping goes away. If there’s more than a tiny jiggle, you’ve got too much. This is why you do it a few times — to “feel” it out. It’s easier than it sounds. Just go to release and add a small bit more. If you’re one of those clowns who actually likes lots of overtravel, then by all means, turn the screw out to your heart’s content.

Now set the sear adjustment screw. With the hammer cocked and red Loctite on the remaining headless screw, turn the screw in until the hammer falls on your thumb. Back it out a bit, recock the hammer, and do it again. Repeat five more times. The bent leg of the hex wrench gives a good clock measurement for this task.

Once you’re sure you know where the trigger breaks — say, 6 o’clock from your vantage point — back the screw out one full turn. Then screw it one-quarter turn back in and stop. This will give you three quarters of a turn of sear engagement.

For safety reasons, don’t reduce this. You’ll find that this is more than adequate and is about one millionth the engagement of a standard factory trigger.

Connect the Disconnector

The author illustrates the correct and only reliable orientations that the hammer and trigger springs are to be installed. Also visible is the polished edge of the trigger pin hole on the trigger.
The author illustrates the correct and only reliable orientations that the hammer and trigger springs are to be installed. Also visible is the polished edge of the trigger pin hole on the trigger.

Now install the hammer pin. Take the disconnector and insert it into its slot on the trigger. If you’re lucky, the whole assembly will work perfectly now. For those of you not so blessed, we now need to time or “fit” the disconnector.

This is arguably the most important piece of the fire control unit. It keeps the gun from slam firing, not firing, and doubling. It happens to be very cheap and easy to replace if you screw this up, as it is also the same part that everyone uses in their semi-auto ARs.

The usual fitting issue involves the disconnector hook on the hammer. It almost always has too much engagement so the trigger won’t reset when it is released.

The solution is very simple. Take the disconnector back out and stone off the tip of the hook on the disconnector a bit at a time until the interference is just barely there. When the hammer is being cocked it should just nick the disconnector. This will give maximum disconnector engagement with the minimal amount of trigger reset.

When you stone that hook on the disconnector, it will slowly become a facet instead of a point. That’s okay, just keep that flat parallel with the trigger pin hole in the disconnector. It’s kind of like finding the North Star by following the imaginary line extending down from the rightmost two stars in the big dipper. Just extend the imaginary line through the center of the hole.

Now put the selector on safe. You can’t do it, can you? You need to take the trigger back out and slowly grind down the safety pad extending from the back of the trigger until, when cocked, the selector will engage on safe with miniscule to no trigger jiggle when safed. The selector should be able to go about halfway to safe when the unit is uncocked.

When this is done, insert the trigger pin, and top the two pins off with their final screws, each with a dab of blue Loctite. This will allow you to get them out later with minor effort, yet will keep the screws from backing out on their own.

Testing the Result

Download the PDF Digital Version of the Gun Digest Book of the AR-15, Vol II
Download the PDF Digital version of the Gun Digest Book of the AR-15, Vol. II. 

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With your thumb in place, cock and fire the trigger multiple times, each time holding the trigger back until the hammer is recocked. Releasing the trigger should then release the hammer from the disconnector, allowing the trigger to fully reset.

If the hammer falls on the block when the trigger is released, then somewhere along the way you took too much material off the front of the disconnector. To remedy this, slowly remove material from the bottom of the nose — that pointy thing on the front of the disconnector — until it will properly engage. The trigger when released should come to rest precisely as the hammer is released from the disconnector.

Once you have that perfect, cock the hammer with the trigger held back to engage the disconnector. Now flick the hammer by pulling it further back and releasing it. The disconnector should catch it. If it doesn’t, try increasing the disconnector hold on the hammer by stoning the nose.

If this doesn’t work, send the whole shebang to JP to have them do it. JP has special triggers held in reserve to fit in receivers with this issue.

The trigger pull should be extremely crisp, light and have no discernable take up or creep. Remember that this is a single stage trigger and will break quickly and cleanly, and has a remarkably short reset.

You may have noticed that there is a lot “take this part out, adjust it, and put it back in” action going on here. If you’re a gunsmith, you should be used to this, and it should be no problem. If you’re not a gunsmith, do it anyway. This is a fire control unit that is designed to be adjusted to your desired settings (safety first overall) and then left alone.

Going in after the fact to change something, other than springs, pretty much involves redoing it. Do it right the first time. Be sure to watch the video. I like to see things done before I actually do them myself.

After initial safety testing, let the Loctite set overnight. Finally, the safety fit can be avoided by using JP’s adjustable selector. Just fit the trigger parts and set the safety with the set screws in the adjustable selector. It saves lots of time.

Go Shoot It

I used to think that standard triggers were not too bad. Not anymore. For the cost of a big sharp-edged free-float Picatinny handguard tube, you can refine the feel of your rifle to a far better result, and improve your accuracy with this JP trigger kit.