Practical Enhancements for Your AR-15–Part 2

headshotBy Mark Foster
Master Gunsmith and AGI Instructor

This is part 2 of 3 of this educational and informative article by Mark Foster on the AR-15, one of the most popular platforms on the market in recent years. In Part 1 Mark discussed barrel selection. This time he moves on to the all-important trigger group!

If you missed Part 1 of this article, look under the “Authors” tab above for Mark’s archives.

Trigger groups:

Standard military trigger groups are practical but not necessarily great. Heavy and creepy trigger pulls are common and resets are usually longer than we might like. They work for general purposes but won’t get you into the winner’s circle of a competition unless they are re-worked. If you want to use your existing hammer / trigger but want to improve it, AGI has a video on trigger jobs for the standard trigger (AGI #335DVD). With the proper tools and procedures, you can eliminate the heavy, creepy standard trigger pull. This is an advanced technique best left to a gunsmith, so if you want a better trigger pull that doesn’t require as much skill, look into two-stage or drop-in triggers.

Two-stage triggers are more expensive than standard triggers but usually deliver a lighter and crisper trigger pull. Great for competition, hunting, law enforcement dedicated marksman rifles, or just to have a better trigger on any rifle. Rock River Arms make a good two-stage trigger but you can expect to pay $125 uninstalled. Geissele Automatics makes, in my opinion, the best two-stage triggers, but they cost $175 or more depending on the model. I have both Rock River Arms and Geissele two-stage triggers and prefer this style on most of my rifles, including law enforcement patrol rifles and hunting rifles. They are practical and tactical rolled into one: a better trigger pull to give you the best chance at accuracy.

Drop-in triggers can be a great way to go because they are easy to install and come in tactical and competition styles. I like Wilson Combat and Chip McCormick drop-in triggers. I’ve used the Wilson Combat TTU trigger in a dedicated marksman rifle with great success. Be careful of a drop-in, or any other trigger group, that has adjustment screws that can back out and prevent the weapon from firing. Not a big deal on the range but it can be a real problem in a law enforcement or personal protection situation when your life is on the line.

AR15Trigger

AR trigger group

Triggers and hammers are fairly easy to replace, especially with the drop-in type. The pins are the same for the hammer and trigger, so they are interchangeable. Be mindful of the direction of the hammer and trigger springs before you remove the pins – they need to go back in the same positions. The hammer spring is formed with a closed “U” on one end and two legs on the other end, with a coil in the middle of each leg. When installed on the hammer, the “U” will be at the top rear of the hammer and the coils will face to the rear. This will allow the coils to get tighter when the hammer is cocked. A major cause of light strikes is putting the hammer spring on backwards, which allows the coils to loosen when the hammer is cocked.

I have a simple way to remember how the hammer spring goes on a hammer. If you look at the spring from the side, you’ll see that the “U” and legs form a line on one side of the coil. If you are right handed, take the spring and hold it in your right hand with the coils to your left. Put your left pointer finger between the two coils, with the closed “U” end up and the legs down. The line of the “U” and legs should be facing the tip of your finger. Now take the hammer in your right hand, with the striking face to the right and the pin hole down. Move the hammer to the tip of your left finger and slip the coils onto each side of the hammer bosses (where the hammer pin hole is located). The “U” will be against the back of the hammer and the legs will extend down and slightly forward. If you are left handed, simply do a “mirror reverse” of the above. This method is used by assemblers at Rock River Arms and it is very quick and easy once you try it.

With the lower receiver separated from the upper receiver, use a 1/8” punch and simply push out the pins. If the pins are difficult to push out, a small plastic hammer can be used to assist. Push out the hammer pin first and the hammer will spring up and out of the receiver. Then remove the trigger pin and remove the disconnector and trigger. The safety selector must be on “Fire” and you may have to tip and wiggle the trigger to pull it out. The disconnector spring usually does not come out of the trigger. The disconnector spring has a flared end that goes into its hole in the trigger and “locks” into place. Bolt catch springs are very similar in size to the disconnector spring but do not have a flared end – be aware of this difference if you have both laying on your bench.

Replace the hammer and trigger in the reverse order but be aware of the spring positions and the disconnector. Place the trigger back into the receiver and drop in the disconnector with the “hook” facing forward. The trigger spring legs should be facing forward and the closed “U” portion should be under the front of the trigger. Carefully align the holes in the receiver with the holes in the trigger and insert the pin. A 1/8” punch can assist with aligning the holes so the pins can be started easier. A hammer is not usually necessary and never attempt to pound the pins in place or damage can occur to the receiver. After replacing the pin, check the trigger to make sure the spring tensions it forward.

When installing the hammer, make sure the two legs of the spring go on top of the trigger pin. This does two things – first it gives the correct amount of spring tension to assure a proper hammer strike, second, there is a groove on the side of the hammer/trigger pins, The spring leg helps prevent the pin from coming out of the receiver. As with the trigger, using a punch will assist with aligning the holes in the hammer and receiver. Most pins will push in with moderate force and a hammer is not usually necessary but can be used with caution.

If you use a two-stage trigger, such as a Geissele, the set will come with hardened pins – use only the pins that come with the set. Install the trigger first, with the trigger spring legs facing forward. Do not use a hammer to beat the pins into place, you can damage the receiver – push the pins into place after aligning the holes. Install the hammer with the legs of the spring resting on top of the trigger pin, align the holes and push in the pins. Test the trigger group and safety to make sure the safety prevents the hammer from falling.

The drop-in triggers are generally as simple as they sound. Remove the old hammer / trigger and replace with the self-contained drop-in hammer / trigger, replace with the new pins and test function the safety.

If you have never replaced an AR trigger/hammer, AGI has a video on the AR-15 (#103DVD) that shows the complete disassembly / reassembly and functioning of the rifle platform.

Keep tuned for Part 3 of this article–we hope you are finding it both useful and entertaining. Personally I can’t wait to see how the story ends–ed.


© 2017 American Gunsmithing Institute. Reproduction of this article by any means without approval is not permitted.


3 Responses to Practical Enhancements for Your AR-15–Part 2

  1. Nicely done sir. I like the write up on the how to’s of removing the trigger. It should make a good guide for all of those on the fence about trying it themselves. I run a Jard in my competition AR and have standard modified military units in my carbines and M16A1 clone. I got lucky on those the sear engagement felt pretty nice for a black rifle and it was EXTREMELY positive. From a safety standpoint I wanted to keep that positive engagement and just lighten the pull a bit, so I just worked on those a bit. I’ll have to check out that trigger job video.

  2. I too have replaced the trigger on one AR. I chose the Timney trigger group for my Bushmaster. Timney is a loose fit and it has two set screws for tightening the trigger group against the retaining pins.
    Other than having to re-tighten the set screws after a shooting session, the trigger pull is great.

  3. Good information Gary. I have noticed a couple things to add to the discussion. About 20% of the AR’s I have worked on, the original trigger would not come out with just wiggling & jiggling. Some I have had to actually remove the safety to gain those last few thousandths of an inch to get the trigger out. Also, when using the original trigger to get the customer an improved trigger feel, a few were not hardened more than a few thousandths deep. So I would get them a nice feel for the trigger, then after a hundred or so rounds, it would develop a gritty feel and the pull weight would start going up. When I got them back and took the trigger out, I could see where the hammer started “eating” away at the trigger face. The only cure was to replace the trigger with one that had better heat treat (and do the trigger job again). Maybe the next one I get in I will start out by heat treating the trigger.

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