Disconnectors from different makers. Notice the variance in the location, shape and quality of the hooks. Some are simply awful. They will all cause different timing issues on the disconnector release.
The trigger is your “go button” for fun and defense. It is also the safety lever, something a lot of people have trouble grasping. The concept, not the lever. There is also a lot of hand wringing and concern that the trigger on an AR is too heavy. The military has some interesting acceptance standards. The allowable trigger pull on the M16/M4 is no lower than 5.5 pounds in all versions. Current M16A2, M16A4 and M4 triggers are allowed to be as high as 8.5 pounds, while the M16A3 and M4A1 may push 9.5 pounds.
Ouch.
And yet, I have used rack-grade AR variants of all sizes, with iron sights, to shoot clean scores on the Army pop-up course, the RETS. It includes shots out to 300 meters. But there is a definite improvement in shooting ability with a good trigger. So lots and lots of shooters look to a replacement trigger to solve their problems. Alas, it isn’t quite that easy. But it does help. However, before we get into the replacement trigger section of this chapter, we’ll spend some time explaining how to properly assemble, install and adjust (if any adjustment is possible) the regular trigger system.
Disconnectors from different makers. Notice the variance in the location, shape and quality of the hooks. Some are simply awful. They will all cause different timing issues on the disconnector release.
The hammer presses directly, by means of its sear notch, on the front corner of the trigger. Your finger pulls the trigger, which pivots around the trigger pin. This in turn pulls the trigger corner directly down off of the hammer notch. Well, not quite directly. The angle of the hammer notch is such that the hammer is slightly cocked as you pull the trigger. More on that in a bit.
To understand just how miserable a leverage system this is, here’s an analogy. Go to the nearest door. Turn the knob and open the door. Easy, right? Now close the door and pull on the door before you turn the knob. Oh, that got a lot harder, didn’t it? That’s the same sort of arrangement going on in your trigger setup. The trigger has to pull the corner down across the surface of the hammer notch while a lateral load is being applied.
And that is why so many people spend so much time trying to reduce the toolmarks on those surfaces, because the lateral load is in effect magnified by each tool mark.
You can see all this if you install the Brownells trigger fixture on your lower receiver (don’t forget the dry-fire block) so you can watch the parts, without the lower receiver walls in the way.
The military trigger on the AR platform is what’s known as a “single stage” trigger. That is, the trigger movement engages the hammer sear directly. It’s also known as a Class One lever. The force applied, and the force exerted, are on opposite sides of the fulcrum, the pivot point. This means that the calculation of force needed is simple. If the distances are the same, then the movement of the effort and load are the same, in distance and work. If the effort side of the lever (the trigger) is twice as far from the fulcrum as the load, the force needed is half, but the distance required to travel is twice as much.
This is also known as a simple lever.
Archimedes knew this when he explained that if he had a place to stand, he could move the earth. Well, he’d also have needed a fulcrum, but when you are boasting, simpler is better.
The engagement surfaces of the trigger and hammer, known as the sear, have a bit more to do with this than might be obvious. The surface of the hammer notch is at an angle to the lever of the trigger, the trigger axis. Also, the front face of the trigger is tilted to the axis of the trigger lever. The result is, if any force less than the total needed to release the hammer is applied, then released, the surfaces cam back to the starting point.
This is the correct installation of the hammer spring. Do it any other way and you will have problems
Let’s assume you have a 6-pound trigger pull on your AR. If you apply 6 pounds, it fires. If you apply 4 pounds, and then let go, you’ll still need 6 pounds next time you pull the trigger. If the engagement surfaces were perpendicular to the axis of the trigger, applying 4 pounds and releasing would result in the trigger and hammer remaining stationary. The next pull would require only the additional 2 pounds.
You don’t have to be obsessed with safety in order to understand how that would be bad. So, the military insisted on the trigger camming back to zero when let go. If you adjust the trigger pull on your AR, you must not change that feature. The mil-spec trigger, as-is, often comes in at the minimum-allowable pull — 5.5 pounds. Which is pretty good, really. Now, if you’re comparing it to a match-conditioned Garand, you’re comparing apples to cinder blocks.
The Garand has what is known as a two-stage trigger. Designed by John Moses Browning (it seems like every time you turn around, Browning was already there) the trigger is another simple lever, with a twist; it has an extra spring-loaded arm. That arm provides the extra force needed to keep the sear surfaces fully engaged.
One way to assemble the lower is to simply shove the hammer in last so the geometry of the assembly holds it in place. This gets it close enough, but still not perfectly aligned.
The trigger with the disconnector properly installed.
Why did the military, and Armalite in the 1950s, feel the design they had was better? I don’t know, but while some feel it is better, or worse, and both camps disagree over this, it is what it is. And the AR trigger is good enough to do what you need. In the modern era, there are also companies who have taken the design, refined the geometry and then surface-treated the parts. A precision-ground AR mil-spec designed trigger, given a high tech low-friction coating, can be surprisingly good — more durable than some two-stage triggers. But, we’ll cover the two-stage triggers in more detail when we get there.
Let’s start from a bare lower receiver, at least bare in that it doesn’t have any internals. Why? Because getting it apart isn’t too difficult and a lot of people seem to think that they must start with the lower empty because they are assembling from a kit or pile of parts. So, we’ll start from a pile of parts.
The trigger and hammer pivot pins come in two flavors, small and large pin. The large-pin lowers are from Colt, made back when Colt was not really sure they wanted to actually be in the gun business. These pins have a diameter of 0.170 inches. Small-pin lowers have mil-spec diameter pins sized 0.154 inches. (This is entirely separate from “large-pin” Colt lower front takedown pins, which are larger than mil-spec. Colt was so weird, for so long.)
The trigger and hammer pins are identical and interchangeable; they are not directional. That is, either end can go into the receiver first from either side. They have two grooves that engage the J-spring in the hammer and hammer spring leg to keep the pins in place in the lower.
Install the trigger spring in the trigger. Position the front loop up underneath the trigger nose, not down on the trigger bow. The spring is tough, so you can bend it quite a bit to make it fit on the trigger. It isn’t indestructible, you can break it, but not easily.
Insert the disconnector spring into the seat in the trigger groove. I know, this is the first we’ve talked of disconnectors, but we’re building from a pile of parts, remember? We’ll cover the disconnector in a bit, but for now stuff the spring in there. Be sure to attach the larger spring loop to the trigger so it stays put. If it falls out, try the other end. If it falls out either way, curse the parts supplier for packing a cheap disconnector spring in the bag and promise yourself you’ll get a proper one later.
Place the trigger in the lower, pushing the first pin across. You want to have a light touch here. The trigger tunnel through which the pin passes has two sharp corners. If you jam the pin in, and hit the corners, you’ll mar the pin. It won’t fit. If you hammer it in, you can damage it. You probably won’t damage the trigger, it is too tough. But the real crime will be when you finish hammering the marred pin into the far side of the receiver. That will chew up the hole, render your receiver inoperable and cost you a new lower. So have a light touch. If it won’t go in by hand, do not pick up a hammer. Find out why.
Some lowers come with the hammer and trigger pin holes drilled to the minimum diameter. Anodizing, the process that makes aluminum tough, causes the surface to grow. A minimum diameter hole, once anodized, becomes below minimum. The pin, if it is near the max allowed diameter, may be a tough fit, even without the trigger to wrestle with. Oil the receiver holes, work the pin in and out a few times and see if you can wear down the high spots. If nothing else, you now know how much force is normal.
Back to assembly. Push the pin in until it captures the trigger, but not past the disconnector slot. Use it as a slave pin. Now push the disconnector down into the slot. Rotate the lower, looking through the hole to check alignment. Move the disconnector around until it lines up with the pin and push the pin across.
Insert the selector lever. Again, first mention. You need a safety/selector. Some lowers (and this is not a brand-by-brand, but a lower-by-lower thing) won’t let you install the safety after the trigger is in. And some won’t let you install the trigger after the safety is in. You’ll have to try the two on your lower and see. Some don’t care: you can install one, then the other, either way. Lucky you.
If the selector fits, great. Pull it back out and set it aside. If it won’t come out, remove the trigger pin and, with the trigger still in the lower, push your selector across. Then re-install the trigger pin. You’ll have to continue with the lever in place. Once you get the hang of this particular dance it gets easy.
With the trigger and disconnector in place, install the hammer spring so the bow is flat to the back of the hammer. Be sure the hammer spring loop bases are forward of the boss on which they ride, not behind. The hammer spring, like the trigger spring, is made tough to withstand bending and to ensure it fits.
Installing the hammer is something those with big thumbs will hate. There are two methods I know of, short of fixtures: self-cocking and thumb-trapping.
The self-cocking method is, hook the hammer spring legs over the trigger pin, with the legs outside of the trigger spring loops. (You always want the legs outside of the loops.) Push the hammer down into the lower, and angle it back into the cocked position. In many lowers, the hammer sear will engage the trigger nose and the hammer will wedge itself into place in the lower. Insert the hammer pin and press it across.
Alas, in too many instances, the hammer stays cocked only until you move it to insert the pin, and then it hurls itself across the room. That’s amusing for the first few times, or until you happen to be looking at it. Trust me on this one, only in romance novels and pirate movies do the ladies get a crush on a man wearing an eye-patch. Don’t lean over the lower, always wear safety glasses and follow my method if your lower does this even once.
The thumb-trap method is as follows: pinch the hammer between thumb and forefinger. Hook the legs over the pin, outside of the loops. Press the hammer into the lower, keeping it upright in the fired position. As it travels into the lower, slide your forefinger into the magazine well — pinching the hammer in place. It can’t escape, but it can cause your thumb and finger a certain amount of discomfort.
To assemble the hammer, with everything else in place, I use the pinch method.
Hold the lower and trapped hammer in one hand, picking up the hammer pin with your other. Adjust the alignment while holding the hammer and moving it to get the pin started when the holes line up. Now stop pinching the hammer. Once in, turn it over, press the pin across, then use the hammer as a lever to align the pin with the second hole, and you’re ready to press it through and flush.
You’ve assembled the hammer and trigger, but you are only halfway done.
Before you proceed any further, be aware of one detail. Don’t let the hammer fall, full-force, with the upper and lower apart. Otherwise you risk damaging the lower. So either do all the testing work with your thumb in the path of the hammer or use a dry-fire block from Brownells.
Cock the hammer. Does it stay in place? Good. (If not, there is either something wrong with your assembly or the parts are awesomely bad.) With thumb in the hammer path, press the trigger. Does the hammer fall? Good. Cock the hammer again and rotate the safety on. Try dry-firing. If it doesn’t fire, you are well on your way to completion. If, however, the safety, when correctly installed, does not keep the hammer from falling when you press the trigger, you have a serious problem.
The safety/selector works by blocking the upward movement of the rear of the trigger. Look at the safety, noting a milled flat. This is the clearance for the trigger when depressed to fire. The safety rotates a quarter-turn, and presents the edge of that shelf, the barrel of the cylinder, to the trigger. This blocks upward movement, keeping the rifle from firing.
If your rifle will fire when on safe, then the rear of the trigger is too low. You can’t build up the safety, it has to pass through the holes in the lower receiver. You can replace the trigger with one that goes on safe when rotated or build up the rear of the trigger. Back in the good ol' days, when parts were hard to come by and were fabulously crappy, I silver-soldered shims onto the rear of the trigger, carefully filing them down to proper size.
Nowadays, I’d simply try the next trigger in the bin or send the trigger back, after checking to make sure it wasn’t the receiver that was at fault. If it’s the receiver, send that puppy back, pronto.
With the Brownells fixture, you get a clear view of the parts and how they function.
One way to check is to use a properly working set of parts from another rifle. If they work in the new lower, then the fault lies with the new parts. If the proper parts now fail in the new receiver, then chances are the new receiver is the problem.
One of the good things about having a properly functioning rifle on hand when building a new one is the opportunity to do checks like that.
Let’s assume yours works fine, and get on with the task.
The disconnector is the flat gizmo that keeps you out of prison. To check it, hold the lower, with thumb in front of the hammer, and dry-fire. Now, while continuing to hold the trigger back, press the hammer back to cock it. Notice that it now is hooked on the disconnector, not the trigger nose. As long as you hold the trigger back, the hammer is trapped. That’s what keeps it from running away in full cyclic mode, expending all your ammo in one exciting, nerve-wracking, expensive and unlawful few seconds.
With your thumb still in the path of the hammer, slowly ease up on trigger pressure. You’ll see the parrot’s beak of the hammer slide off of the disconnector nose and let go. If the disconnector is properly timed, the hammer will be captured by the trigger nose and you’re good to go.
The disconnector spring, in an M16 trigger (the open end of the rear tells us that) and ready for a disconnector.
What is meant by disconnector timing? As you ease up on the trigger, it rotates, slowly coming to the point where the disconnector lets go of the hammer. The trigger nose, or sear, rises into the path of the hammer notch. If the trigger/disconnector lets go of the hammer too early, the trigger will not have lifted high enough to catch the hammer. Two shots will be fired — one when you pull and one when you release. Some rifles have an early timed disconnector, but their owners don’t know it. They don’t know it because they have only ever fired by pulling the trigger back, and then releasing it as quickly as possible. The trigger spring, in full power, has enough oomph to push the sear into the hammer notch path. However, when the same shooter, with the same rifle, tries to do accuracy work off the bench, they may ease the trigger forward. Holding the trigger back from full release, the early timing causes the hammer notch to miss, or bounce, over the trigger and fire. Oops.
At the opposite end, a late disconnector releases only when the trigger has fully risen up into the hammer notch path. You’d think, “Cool, late is what I want.” No, you don’t. You see, the engagement surfaces of the hammer and disconnector may have machine tool and stamping marks on them.
The disconnector in particular is a source of misery. You see, it is produced by a process known as fineblanking. This is a refinement of the punching process, which produces products with a cleaner edge. However “cleaner” is the operative word. The end result is a relatively straight, relatively clean-edged part that requires no further treatment besides hardening and surface finishing. In some applications (not necessarily firearms), even the hardening process isn’t needed, depending on the alloy used and the application. The result is a disconnector hook that is not correctly shaped with a rough underside surface.
The hammer, meanwhile, is cast and then machined. The hammer’s hook can have what is known as a wire-edge, where the last cut caused a tiny curl of steel to form on its end.
Combine the wide edge and the rough surface of the disconnector with a late-timed setup, and you can have a disconnector that never lets go.
So, ideally you want a disconnector that releases the hammer past the half-way point of trigger movement, but does so no matter how slowly you ease off on the trigger.
Changing early disconnector timing is easy. The disconnector is timed to the trigger by its engagement with the trigger underneath the front tab of the disconnector — the angle that juts forward, below the hook. The underside of that surface is your target. A clean, sharp file is all you need. Typically, disconnectors are made of 4130 steel, which is hardenable, but except for the top-tier (and I hated typing that, but here it does apply) manufacturers, it is usually only surface-hardened.
Simply take the disconnector out, turn it upside down and clamp it into your bench vise. Take a couple of passes along that surface to clean it up — the rough surface might be a big part of your problem — and to remove metal to adjust the surface location.
Top, the M16 disconnector, bottom the AR-15 semi-auto disconnector. Grind off the tail of the M16 disconnector, and you have an AR version, which is exactly what the factory does.
Reinstall the disconnector and check timing. You’ll probably find it has changed a little.
Repeat until the disconnector releases late of the halfway point, but not at the end of the trigger movement. Wait, you aren’t done. Pull the disconnector out one last time, knocking the burrs off the edges with your file, making sure the disconnector moves freely in the trigger slot. You can also cold-blue the surface if you want, but no one will notice. While you have the disconnector out, gently hone the undersurface of the hook with a medium coarse stone. You are not looking to change the timing, just smooth the surface if it is rough. While you’re at it, look at the hammer hook, and see if there’s a wire edge to it. If so, stone that, too.
What if the disconnector is late? My first choice would be to swap disconnectors until one is found that isn’t late. However, if you have only one, then you can adjust timing on a late disconnector. Your target here is not the underside of the disconnector nose, but its tip. The underside can only make it smoother, not change the timing. By trimming the disconnector nose you allow it to release the hammer sooner.
Use a stone to smooth under the disconnector nose and, if there is one, the wire edge from the hammer. A simple smoothing over of these could solve the problem of a late-timed disconnector.
If not, then you have to adjust the disconnector nose tip. You must take more care here than in filing to correct an early release. The amount of metal removal needed to correct late timing is much less than the amount needed to correct early timing. File just a tiny amount, reinstall and check timing, repeating process until correct.
Once the disconnector is timed and the safety passes its check, you’re done with the mil-spec trigger installation. But what if the mil-spec trigger is too heavy?
Some claim you should not polish, stone or otherwise adjust the mil-spec trigger, because it is soft inside and will wear quickly if you cut though the outer layer. As with many things, this does have a kernel of truth, but for the most part it isn’t the case.
I asked an industry insider who makes mil-spec parts about this. The response surprised me. The hammer is composed of an alloy known as 8620. This is a chrome-moly-nickel alloy that takes carburizing well. 8620 is known for its very good casting characteristics. That the hammer and trigger are cast should not be seen as a defect. The casting does not usually need to be heat treated, as 8620 is an air-hardening alloy. That means it does not have to be quenched, only air cooled, which causes the crystalline structure to form in a hardened state.
Once cooled, the parts are treated for carburizing, introducing additional carbon into the surface for extra hardness and wear durability. This hard surface, called “case hardened” in the old days, is listed in the mil-spec as being 0.014 to 0.018 inches thick. The parts are parkerized for corrosion resistance and then we come to the dicey part. The hammer hook and trigger face are machined or ground to create the engagement surfaces. This can remove half or more of the hardened layer, leaving a much thinner hardened layer on the engagement surfaces.
Unless you are using power tools, you will be hard pressed to polish through .014 inches of hardened steel. However, if only half that amount is left, say .007, the chance of problems increases. How thick is .007 inches? That crisp new dollar bill in your pocket is .0045 inches thick. So, just under two of those. Ouch.
It is possible for someone with a good stoning fixture, steady hands and much patience to clean off the toolmarks on the engagement surfaces to improve the trigger pull. But if one thing goes wrong here, you have a rifle that doubles — firing two shots with one pull of the trigger.
As a result, I can’t in good conscience recommend that you go polishing on the hammer hook and trigger nose of your AR. Why? What can go wrong? For one, you might change the negative angles on them. Those are the angles that cause return to full engagement if you pull the trigger part way and then release. Second, if you do go too far, and end up with incorrectly polished parts, you’ll have created a two-shot or more AR. And that, ladies and gentlemen, is the exact legal definition of a machine gun.
Which is the main reason we don’t go messing around with the mil-spec parts. If the parts are all original, and unaltered, and you have a rifle that occasionally goes burp, then you have a solid explanation: the parts are bad. If you’ve polished, stoned, filed, ground or otherwise worked on them, then it’s all on you. Good luck with that, because people have been sent to prison for just that very thing.
Can you improve the trigger pull with some careful polishing? Yes, but do not expect anything magical as a result. If you’re careful you can remove the grittiness, but you are not going to make an 8-pound trigger a 3-pound one with some polishing. No, for that you’ll have to replace the parts with something non-mil-spec.
The best solution to tuning mil-spec triggers is to swap out the crusty USGI parts for a hammer and trigger that have been made with the engagement surfaces properly polished. If you want to do more than that, you can reduce the hammer mass or the hammer spring power.
Colt took the first approach, producing a match trigger that was a simple stub of the usual GI hammer. They chopped off the hook on the back, leaving the upright stick as the hammer. This cut the mass of the hammer in half, which increased speed, reduced lock time and retained primer impact force. (You might have a problem with really hard, military surplus primers. However, the supply of those has long been used up in surplus ammo.)
This is the notch on the upper corner of the hammer, which Colt designed to prevent hammer-follow full-auto fire.
In the early days, I took this approach myself. I had the happy situation of a set of bins filled with hammers, triggers and disconnectors and I could swap them around until I found a set that worked well. For the match rifles, I used a mill or cutoff wheel, making the hammer just an upright vestige of itself.
However, lightening the hammer does not address the weight of trigger pull. So, I figured out a way to bend the existing hammer spring to lighten the lateral force on the engagement surfaces. Now you can simply buy lighter-power hammer springs from many sources (I suggest Brownells) and use those.
Don’t tinker with the trigger spring. It would seem that taking the force directly out of the trigger pull would have better effect. Yes, but the trigger spring is also the trigger return spring, and by reducing its strength, you slow its return up into the path of the hammer notch. It’s true that a properly timed disconnector will not release the hammer until the trigger nose is in the path of the hammer notch. But I like insurance.
Also, I first tried the reduced hammer spring approach, it worked and worked well, so I never bothered with the trigger spring.
For a proper trigger pull, you need to replace everything with the exception perhaps of the safety. Trigger replacements come in four different versions — improved mil-spec, improved non-mil-spec, two-stage and self-contained or packet triggers. The packet triggers can be had in either single- or two-stage.
Black Rain Ordnance also makes a packet trigger assembly.
Added to the other Colt problems is the trigger pin issue. In order to prevent the use of full-auto parts (not that there was an epidemic of such actually happening) Colt tried to adopt a new “civilian-only” standard. The regular, mil-spec trigger and hammer pins are a nominal 0.154 inches in diameter. Colt made the new standard 0.170-inch pins.
New rifles would not accept the old pins, and old rifles were beyond Colt’s control. Well, if you have one of those old Colts, your only choice is to use large pin components. Back in the day, that meant you were stuck with whatever God-awful crap Colt decided to put into a so-called civilian rifle, and any replacement parts you might track down were made in the same place … Colt.
Now days you have choices. Not as many as you’d have had with rifles using the regular small pins, but you do have choices.
The Brownells dry-fire, trigger-adjustment and learning fixture. That was too long a name, but that’s what it does.
Improved mil-spec are hammer/trigger sets (some come with disconnectors, some don’t) that have been built on the same pattern but with greater care. The surfaces might be ground and polished before hardening. The parts might be plated with a high tech corrosion-protection and lubricity plating. They can be fully machined from bar stock, rather than castings that have been touched up on engagement surfaces.
Examples include the JP Enterprises original trigger, parts that started the design process looking like USGI, with added adjustment screws to let you tune in sear engagement, overtravel and the ability to swap spring strengths.
Improved non-mil-spec triggers are epitomized by Geissele, a company that went even further. While most Geissele triggers are non-adjustable, they took the USGI design, tightened the operating dimensions, made the hammer, trigger and disconnectors out of better steel and precision ground the engagement surfaces. Interestingly, despite my classifying them as non-mil-spec (due to the appearance, dimensions and tolerances) they came about because military special ops wanted better triggers.
The disconnector does double duty on a two-stage trigger. It first captures the hammer on the cocking stroke. Then it acts as a spring-loaded trigger stop to control trigger pull at a low level, while keeping the hammer fully controlled. The original comes to us from John Moses Browning and the Auto 5 shotgun. Since then it has been adopted, stolen and adapted to a host of rifles and shotguns, from the Remington Model 8 to the M1 Garand and the AK-47.
Brownells fixture with ALG trigger parts installed.
How the two-stage trigger works. When the action cocks the hammer, the rear hook of the hammer catches on the disconnector.
To see how it works, make sure your gun is unloaded. Start with the hammer cocked, safety off, and your finger depressing the trigger. Note the upside-down “T” at the hammer’s engagement notches. The trigger has a pair of hooks. The front hook is the trigger sear, the rearward hook the disconnector and second step. An important point: these two sear surfaces are not the same distance from the trigger pivot, the trigger pin. The disconnector hook is slightly higher and farther from the pivot point.
As you release the trigger, the disconnector "hands off” the hammer from the rear hook to the front hook.
When you pull the trigger, the hammer hooks on the forward trigger sear and, as you pull, the trigger sear slides forward, toward release. But, once it gets halfway there (or so) the rear arm of the hammer T bumps up against the disconnector.
The disconnector is hinged in the trigger (not on the trigger pivot point) and has its own spring. In order for the trigger to keep moving and release the hammer, it must pivot the disconnector back out of the way. This is the second stage of the two-stage trigger system.
This means you can have a very light, smooth, even delicate engagement between the trigger sear and the hammer sear, and the trigger pull weight will be regulated by the force of the disconnector spring pushing in the second stage.
You complete the pull, the hammer is released and the rifle fires. Your finger completes the pull, remaining there as the hammer re-cocks.
When the hammer comes back in cocking, the trigger sear is out of the way. But the disconnector, pushed by its own spring, has pivoted forward and the rear arm of the hammer T now hooks onto the disconnector.
When you release the trigger, the disconnector pivots back, releasing the hammer T. But before the disconnector can release, the trigger hook slips over the hammer hook and the disconnector hands off the hammer to the trigger.
You are now back to where you started.
A two-stage trigger pull feels different than a single stage. As you pull a single-stage trigger, the required weight increases in a more-or-less smooth rate until you reach the release point and the hammer falls.
As you pull the trigger, the first stage is the hammer hook sliding on the sear. The second stage begins when the rear of the hammer hits the disconnector. At this point, the second stage pull is applied against the disconnector spring.
In a two-stage trigger, you press back with half the force you need for release (more or less) until you feel a mechanical stop. That’s the disconnector nose bumping the hammer T. Then you add the rest of the pull weight for release. Except, it doesn’t feel like you have to add weight since your trigger finger is already pulling a certain weight and your brain and trigger finger accept that as normal, and thus, zero. The extra weight is all you feel.
As a result, let’s compare two 5-pound trigger pulls. On the single-stage, you pull and pull and, once you get to 5 pounds, the hammer falls. On the two-stage, you pull at 2 pounds until you hit the stop. Then your brain forgets those 2 pounds and you only feel the next 3 pounds needed to push the disconnector back.
In effect, the two-stage trigger has the mechanical safety of a 5-pound trigger, while feeling like a 3-pound trigger.
It is important to remember that on a single-stage trigger, disconnector geometry is what controls early or late timing. The two-stage trigger also has a geometric determinant of timing, but the parts are so much closer to each other, it's simpler for manufacturers to maintain correct timing. Also, the parts maker produces all of the parts. In the single-stage design, the trigger and the disconnector makers may not be within a thousand miles of each other. Two-stage triggers are made as complete sets, in the same shop, thus it's very unlikely to find an incorrectly timed disconnector in such a design.
Single-stage trigger pull weight is determined both by the strength of the trigger spring and the smoothness of the engagement surfaces. The single-stage requires a strong trigger spring in order to keep the trigger lifting quickly enough to intercept the hammer notch. In a two-stage trigger, while the geometry has to be correct, the force of the disconnector spring determines pull weight. The disconnector spring does not have to be strong to ensure hammer notch interception.
One of the problems with the AR-15 is that it has been made by a slew of manufacturers. That’s good, in that a wide industrial base makes it difficult to put a crimp on things. Were AR-15s only being made by Colt, and only being supplied by one aluminum forging shop, the defense efforts of the US could screech to a halt from the slightest disruption in supply chain.
But unless the myriad of shops that make ARs all have the same blueprints or CAD/CAM data, and unless they are all regularly inspected, dimensions will wander. Trigger pull can vary depending on the particular lower into which the parts are dropped. No, there is no list of good, average and bad lowers. Rest assured, though, that for the big-name makers, dimensions do wander. The locations of the hammer and trigger holes can vary simply because a shop doesn’t have the actual USGI blueprints. They may have taken in lowers made by Colt (who else?) and measured them to come up with as-close-as-they-can dimensions.
If dimensions vary by a few thousandths, that difference can have a big impact on felt trigger pull.
Packet triggers — which can be either single- or two-stage — avoid these issues. Think of a package with all the working parts in a self-contained envelope, one that does not depend on pin hole location accuracy, and then every single one you make will have the same trigger pull. This voids the problem of off-center pin holes. The packet utilizes tubes in which the hammer and trigger/disconnector pivot. The tube’s hole is larger than the regular hammer and trigger pins. The packet essentially floats on the two pins, finding its own center. The clever makers (and they are all clever, one way or another) use spring clips to catch the grooves in the standard pins, which keeps the packet in place and the pins from falling out.
Since the hammer and trigger pivot on the tubes, and the tubes are fixed to the packet, the maker has absolute control over the dimensions. In such a situation, it is possible to make the trigger pull in the packet pretty much anything you want, within the limits of material and design.
The main thing to remember about the various packet designs is, they are not user-serviceable. They were not designed to be disassembled by you. Your maintenance will consist only of prying the packet out of an encrusted jacket of carbon, scrubbing, hosing, degreasing, scrubbing some more, oiling and re-installing after you’ve shoveled the carbon out of the lower.
You can't adjust trigger weight, overtravel, etc. All that has been done for you, that’s why you bought a packet-design trigger system. If you wanted one that had a half-pound less weight, you should have selected that one from the drop-down menu when you ordered it.
The installation of improved mil-spec triggers is exactly like that of the mil-spec variety, with one caveat. If you do any filing, stoning or other changes, you’ll have voided the warranty. If you take a precision-machined, plated trigger system, and drop it into your lower, and find it does not work properly, the odds are good it is your lower that is at fault.
There are no lack of improved mil-spec parts, and you can find them pretty much everywhere.
The Quality Mil-Spec trigger, or QMS in ALG-speak, is at first blush just a set of mil-spec parts. However, ALG has taken the basic forging/casting and precision machined the engagement surfaces of the trigger and hammer. This produces a trigger with a weight no less than mil-spec (a rated 5.5 pounds minimum) but eliminates the grit, creep, toolmarks and other problems that a fully mil-spec (and thus lowest bidder) trigger pull presents.
ALG Defense offers a box-stock trigger, but with a cleaner pull.
This comes to you for the amazing price of $49.00 (2016). That’s pretty much what the one-stock mil-spec parts would cost if you were to haul yourself off to the next gun show and peruse the bins of parts on the tables there.
So save yourself the hassle and just get the ALG if you need a box-stock looking parts set that delivers a clean trigger pull.
If you take ALG’s QMS, clean and smooth the engagement surfaces and differentially plate the parts, the end result is the Advanced Combat Trigger, or ACT. While the pull weight is not reduced below mil-spec, its smoothness will fool you into thinking that is the case. Dry-fire it, and you’ll swear it’s a 4-pound trigger. Then go and hang some NRA weights on it and find that it holds 5.5 pounds.
The ALG Defense Advanced Combat Trigger. The same parts as GI, but the sear surfaces are ground to a better finish and are plated.
The trigger is given a nickel-boron coating, which imparts impressive wear resistance, in addition to being harder than an IRS auditor’s heart. The hammer is given a nickel-Teflon plating. The Ni-PTFE coating, while not as hard as the nickel-boron, has a pleasing lubricity, easing the trigger pull. As a bonus, ALG plates the disconnector and the pivot pins in the nickel-Teflon as well.
If your agency or department doesn’t allow non-GI parts, that’s a problem, I’ll admit. But, what they really are getting at (and the regs may even be written this way) is no external modifications, or modifications that require a trained armorer.
The big advantage to nickel-boron coating is that it can be painted. You can spray paint the trigger bow a flat black and it will not be externally modified. Just be sure to mask the trigger so you don’t paint the sear.
The Advanced Combat Trigger gives you a clean, crisp 5.5 pounds minimum pull, yet from the outside looks like a standard trigger. In fact, it would be the standard trigger today, if the Neanderthals in DoD had spent the last half-century actually improving the M16.
Alexander arms improves the single-stage. Not only is the hammer lightened, the disconnector skeletonized, and the surfaces polished, but there are engagement and overtravel screws for adjustments.
Alexander takes the single-stage trigger and improves it. First, the engagement surfaces are cut and polished to perfection. Then unessential mass is cut away from a standard hammer. A lightened hammer reduces lock time as the spring has less mass to accelerate. The impact of the hammer on the firing pin is less, reducing vibration and error-inducing problems. And the firing pin moves faster (law of conservation of momentum), reducing lock time.
There are two adjustments, one for sear engagement, the other for overtravel. They are adjusted in the same manner as the JP trigger. You have a choice of standard or blade trigger bow.
The original JP trigger is a highly modified single-stage trigger that also looks like a regular GI part, but with a closer examination exudes good engineering. The JPFC-1 is a refined single-stage that can be tuned to produce a very good, even exemplary competition trigger — especially when combined with a JP speed hammer.
The engagement surfaces have been precision ground and the angles have been adjusted, reduced to the cam-on-trigger-pull geometry of the USGI engagement surfaces. Select the appropriate spring weights and engagement dimensions and you can make a super competition trigger, or a very good and useable one for duty or defense.
The JP Enterprises trigger can be installed using their locking pins. If you’ve gone to the trouble of making it perfect, you should make sure it stays that way.
But to achieve this you must tune the parts to each other in the receiver in which they will be used. There is no “one tune fits them all” solution.
The adjustment screws on the trigger allow you to fine tune sear engagement, overtravel, and disconnector timing. The springs adjust pull weight.
As is usual with JP, the support is overkill. Not only are there complete instructions, but a DVD video and — if all that wasn’t enough — the option of having JP do it for you. As long as you haven’t done any stoning, filing, grinding or other unalterable changes, you can just pack up your lower and the JP parts, ship them off and JP will assemble it for you. It takes a week, they charge a small fee and you have it done right.
The JP Enterprises original trigger: adjustable, a good learning tool and a great product.
Double check as always that the gun is unloaded. Do a preliminary check-fit to make sure all the parts will go into the lower receiver. Your receiver may be machined too narrow, the trigger and hammer might not fit. If everything fits, you can begin.
Install a dry-fire stop in the magazine well, such as the Brownells.
Install the hammer and trigger. Leave the disconnector out for the moment. Cock the hammer. Use the supplied wrench, turning the overtravel screw down until it stops. No matter how hard you press the trigger, the hammer won’t fall. Now, rotate the overtravel screw out (upwards) until it clears the hammer and you can dry-fire.
The original JP trigger has adjustment screws. Located in the front, this is the sear engagement screw.
At this point you have to make a decision. The less overtravel you have, the cleaner, crisper, and all-around better your trigger pull will be. It will also be less forgiving of dust, dirt, crud, carbon build-up and anything else that is determined to get in the way. Also, a minimal no overtravel situation can cause you problems if you fail to reset the trigger crisply.
Remember, the JP trigger is meant as a competition trigger, for 3-Gun and DCM. It is not meant for duty or defensive applications.
Adjust the sear engagement screw. (This is the one in the rear of the trigger.) Cock the hammer. Adjust the sear engagement screw until it pushes the trigger out of engagement and the hammer falls. This is the release point. With the hammer forward, JP recommends that you back the engagement screw from the release point by three-quarters of a turn. They suggest that the absolute minimum for competition use is a half-turn, but I’d add to that. For me, the absolute minimum is three-quarters, and I’m much happier with a full rotation back, for best sear engagement.
Recock the hammer and check the trigger feel. Decide if it meets your standards for competition use. Install and time the disconnector, as we’ve outlined earlier. Except, with the JP trigger, the supplied disconnector isn’t a half-mangled stamping but a precision-machined piece of hardened steel plate. The job should be easier, but you still need to check the timing, correcting any early or late release.
Last, fit the safety. JP ships with the trigger tail machined a bit on the high side. You do not need to remove the hammer. The now-adjusted overtravel and engagement screws keep the trigger exactly where it should be and the hammer will not be a hindrance, except to install and remove as you go to do your filing. If you cannot get the safety to rotate to Safe, then you’re all set. Carefully and gradually file the top deck of the trigger tail until it just clears the safety. The correct fit is achieved when the safety top clicks into place without binding, but with no trigger movement at all once the safety has been applied.
To adjust the weight of the trigger pull, JP offers springs of different strength, color-coded with paint. Adjustable weight ranges from a low of 3.5 pounds, up to the 4.5 pounds required by CMP competition. And as if all that wasn’t enough, JP offers locking hammer and trigger pins. They come with headed screws that you tighten (you can use Loctite if you wish) to make sure the pins don’t move.
Geissele (pronounced “guys-lee”) sprang onto the scene making triggers for bearded guys who went to dusty places, there administering justice to unrepentant medieval whackjobs. Once things were made to his — and the professionals' — satisfaction, Geissele marketed triggers to the rest of us. Which works for me.
Geissele makes a demo fixture for their triggers, so you can see how they work and feel the trigger pull for yourself. This is a two-stage trigger.
The company makes 21 different triggers as of this writing, most of which are for the AR in one version or another.
The S3G is a derivative of the Super Select-Fire (SSF) trigger, which Geissele made for special operations teams. That’s right, a machine gun with a target trigger. Actually, you targeted in semi-auto mode and, when you flipped the giggle switch, trigger pull became less an individual event and more a hose on demand option. 3-Gun competition isn’t full-auto, but you can still heat up a rifle quickly. And you have to hit what you are aiming at or your score suffers.
The Geissele Super 3-Gun trigger, ready to drop into your lower receiver.
So, Geissele took the SSF, removed the select-fire knobs and extensions, and produced the two-stage Super 3-Gun from it.
Its trigger pull comes in at right around 4 pounds. You can ease that up if you use a lighter hammer spring, but you wind up increasing lock time.
Aside from changing trigger and/or hammer springs, there is no adjustment in the S3G.
For National Match competition and the Designated Marksman program, the military decided during the war in Iraq and Afghanistan that trigger pull matters.
The Geissele Hi-Speed NM-DMR is an adjustable two-stage trigger. Each one comes with detailed instructions. There are a few things that you must attend to and be aware of with this product. It's not a simple drop-in installation.
First, use only the included hammer pin, not the mil-spec GI pin you removed. Also, the Geissele pin is installed from the left side, and its retaining groove must be on the left side of center.
Second, make sure the safety selector blocks the trigger before you start adjusting things. If the lower receiver is off so much that the safety won’t work, you need to be looking at a different rifle, not carving on the Geissele.
And finally, the Geissele trigger needs proper clearance in the lower. Assure correct fit of the lower's oval through which the trigger bow pokes. It is not unusual for the oval to be excessively machined — the specs on this assume a mil-spec trigger, and we know what mil-spec means — such that the Geissele bow contacts the edge of the oval.
The Geissele High-Speed NM Trigger, complete with extra springs, assembly tool and adjustment wrenches.
If there is a problem, it’s a conundrum. The standard gunsmith fitting process is to cut on the cheaper, easily replaceable part, to make things fit. A new lower costs less than a new Geissele. But, the lower is the serial-numbered part, and more difficult to replace if you make a mistake (especially in some jurisdictions).
Me, I’d cut the lower, since aluminum is softer and easier to trim than hardened steel.
Last, follow the instructions for adjusting overtravel and sear engagement. You can remove all the overtravel, but if you do, you pretty much make the rifle useless. Even a change in temperature can mean your no-overtravel situation becomes a … no-travel situation. And, you want to ensure enough sear engagement to keep the rifle drop-safe.
The MBT-2S (Meticulously Built Trigger) is crafted from S7 tool steel. As in, take a plate of pre-hardened tool steel and cut triggers, disconnectors and hammers out of it. Then, have the in-house toolmakers assemble and test each one before packing and shipping.
Tool steel is incredibly hard, and wears like … tool steel.
Geissele makes two-stage triggers for all uses and occasions.
As a two-stage trigger, the MBT-2S has an initial pull of 2.5 pounds, followed by a break at 2 pounds more. It is for small-pin lowers only and cannot be adjusted. It comes with pins and springs in a nifty padded shipping can with clear top so you can see exactly what you’re getting.
Installation is simple, and is exactly like that of a mil-spec set of parts — except when you’re done you get a marvelous trigger pull.
The first packet trigger came to us from Chip McCormick Custom, or CMC. It was fabulous. No more tuning, adjusting or fiddling with the disconnector. The trigger pull was what it was, regardless of what lower you installed it in.
There were drawbacks. The stamped sheet steel shell was not always an easy fit in some rifles. Perhaps I have too many legacy guns, made decades ago by people no longer in the business, but in some of them the CMC was a tight fit. (In one, it wouldn’t fit at all.)
One of the very first Chip McCormick packet triggers.
But that was changed a few years ago and the new units are much better. They fit all the current lowers and you have choices. The first choice you need to make is single- or two-stage.
In single-stage, pick a trigger weight, any of four weights, from 3.5 to 6.5 pounds, in full-pound increments (3.5, 4.5, 5.5, 6.5 pounds). Then choose between curved or straight trigger.
For two-stage, choose either 1 pound on the slack and 3 pounds on the pull, or 2 pounds on the slack and 2 on the pull. Curved or straight trigger is the other option here.
The Wilson Combat Tactical Trigger Unit is a single-stage, semi-auto packet trigger. To install, yank out the old parts. Slide the TR-TTU in, making sure it clears the selector. If it doesn’t, remove the pistol grip. Put in the TR-TTU, placing the selector back. Don’t lose the selector spring and plunger.
One of the big advances that came along when we moved from stamped to machined aluminum shells, was the inclusion of “D” clips. The D clips catch on the grooves in the hammer and trigger pins, keeping them in place.
The Wilson Combat TR-TTU packet trigger.
The hammer, trigger and disconnector are wire-EDM cut; the shell is CNC machined and there are no adjustments. The Wilson Combat trigger comes with hammer and trigger pins, so if you are building from scratch you don’t have to source those as extras. You can use the Wilson parts or the ones you already have. Either will work.
As a bonus, the TR-TTU has a half-cock notch, much like that of the 1911 pistol. If you are worried about a discharge when the rifle is dropped, the Wilson Combat trigger takes care of that. Should the hammer jump the sear when dropped with nothing holding the trigger back, the half-cock notch will catch the hammer without firing.
If the 4 pound weight of the TR-TTU isn’t to your liking, Wilson makes packet triggers in an array of weights and as two-stage variety as well. In all, five different units are available, with weights from 3.5 to 5.75 pounds.
The Tac-Con trigger is a neat bit of gear. First of all, it is a packet trigger in a machined aluminum shell sporting precision made hammer, trigger and disconnector. The internals are wire-EDM cut from precision-ground pre-hardened stock. The working parts are given a plating of NP3, a nickel-teflon self-lubricating coating. The pin tunnels have built-in “D” clips, hammer and trigger pins held in place by the packet. And the single-stage design provides a clean, crisp 4.5 pound trigger pull.
Tac-Con supplies a packet trigger and a replacement safety.
The third mode of the Tac-Con is a positive reset. The mechanism uses the power of the cycling carrier to reset the hammer-sear engagement, reducing the split time between shots. It isn’t full-auto, and Tac-Con has the letter from the ATF proving it, but it is such a high cyclic rate that someone who didn’t know better would think you had one.
It is a clean, crisp trigger pull, which can make a difference in your scores in a competition.
To install, pull out the old parts, plug in the Tac-Con, make sure it plays well with the safety/selector and doesn’t bind in the lower receiver and you’re done.
One of the first, if not the first, packet trigger makers after Chip McCormick, American Gold went with wire-EDM internals and an aluminum shell. To give you an idea of how good it is and how much of a change it can produce in your AR, consider Jerry Miculek. Considered (rightly) to be the best revolver shooter who ever lived, Jerry is also a really good all-around shot, and a serious 3-Gun competitor.
The American Gold packet trigger model that Jerry Miculek used to win the 3-Gun Nationals.
American Gold sent him a trigger to try out. He plugged it into his competition rifle a couple of weeks before an upcoming USPSA 3-Gun Nationals. It made such a difference that he left it in, went to the Nationals, won, and told American Gold they weren’t getting their trigger back.
It’s a packet trigger, installation is easy, as covered earlier.
Timney has been making replacement triggers for what seems like forever. When a hunter wanted a good trigger on an inexpensive, military surplus rifle, he went to Timney. When taste in rifles shifted from bolt guns to self-loaders, Timney paid attention, releasing a line of AR triggers.
The Timney packet trigger.
Offering both single- and two-stage triggers, the Timney design is consistent across models — a machined aluminum shell with precision wire-EDM cut S7 tool steel parts.
To install, do all the regular steps; pull out the old, check the fit of the trigger to the safety and the trigger clearance oval before putting it back together.
Where the Timney design differs, is in how it secures the packet inside the receiver. Instead of “D” clips on the pin tunnels, set-screws are used to press the packet up, employing the bottom interior of the lower receiver as the push-plate.
The process isn’t difficult. Make sure everything fits, press the Timney down into the receiver and push the hammer and trigger pins through. You can use a bit of masking or painter’s tape to hold them in place. Use the included Allen wrench to tighten the set screws, which lifts the packet, and pins the hammer and trigger pins into position.
Timney is careful to explain that if you have a polymer material lower, you should put a thin aluminum plate underneath the trigger as a bearing surface for the screws. Otherwise, they will gouge the receiver and fail to lock into place.
Note the two securing setscrews on the bottom of the Timney housing.
Me, I’d add another step. Once the Timney is secured, and you’ve test fired it enough to know that it works, degrease the interior and apply dabs of paint to lock the set screws in place. You don’t want to use wicking Loctite, because you might want to remove the packet at some future date. Paint will lock the screws and indicate if any break loose.
After swapping, tuning and adjusting your parts, must make sure they work properly. Here’s the process. Make sure the rifle is unloaded, and that no loaded magazines or loose ammo are anywhere nearby.
Close the bolt, turning the safety on. Depress the trigger, putting at least 10 pounds into it. Let go of the trigger, and then turn the selector to Fire. If the hammer drops, you’ve got problems. If the hammer doesn’t fall, proceed.
Dry fire the rifle, holding the trigger to the rear. Work the charging handle to cycle the bolt. Pull the charging handle back, then ride it forward. Yes, you are not supposed to be riding the handle, usually, but we’re checking one thing at a time here. Slowly ease the trigger forward. You should hear and feel a click when the disconnector hands the hammer off to the trigger nose. If there is a loud “clack” sound as the hammer falls on the firing pin, you have a problem. If normal, proceed.
Dry fire again. When you hold the trigger back, yank the charging handle back hard and let go, in one motion. Ease the trigger forward. No click? Good.
Put the safety on and lock the bolt back. Use the hold-open button, and release the bolt so it crashes home with full force. Turn the selector to Fire, and dry fire again. The trigger pull should be normal.
Now for the potentially abusive part. Leave the selector on Fire. Lock the bolt back, then push the button and let it crash home. Dry fire. If the trigger pull is normal, you are done with dry testing.
If at any time during this process the trigger pull changes, or the hammer falls when you don’t intend it to, you have erred in trigger pull tuning and need to go back and do it again.
If you do the function check and find your rifle doesn’t work properly, you have to dive in and see why. For this, the Brownells Dryfire Jig is very, very useful. It allows you to mount the parts on the exterior of the lower you will use. That way, if there is some anomaly in your receiver that is causing the problem, you can see it.
The jig is easy to use. Employ the long pins to hold the jig on the side of the receiver. Place the parts in the jig, in effect assembling them outside of the lower. Then watch while you re-create the problem that happened during the function test.
You can experience a hammer drop either with the safety on when you press the trigger, or when you press, release and rotate the safety. The problem is usually the trigger. It can be caused when the trigger is too short on the back end, with too much clearance between it and the safety (there should be none when the selector is set on Safe). It can also happen when the trigger pin hole is in the wrong place.
If it's a trigger pin hole issue, you have no options. Send the lower back for replacement. You haven’t done anything to it, have you?
If the problem is the trigger, you can swap out the offending one for another with the proper dimensions on the rear. Failing that, you can use a high-temp silver solder to fabricate a thin piece of steel on the backend top of the trigger. File the solder until it is only tall enough to block trigger movement, but not so tall it keeps the safety form being turned to Safe.
This happened on rare occasions back in the early days. Today it is unheard of. The last time I mentioned it in an armorer’s class, the students collectively looked at me like I was describing how to knap flint.
This is easy, it is an early disconnector, which we’ve discussed before. Simply time the disconnector correctly.
This is due to minimal sear engagement, or a trigger spring that is too light. If the sear engagement is minimal, this is a geometric problem caused by the hammer, the trigger or the receiver pin holes. Whichever it is, replace.
It is possible that the trigger spring is too light. If you think that is the case, replace it with a new full power, USGI spring and test again. If it still happens, then the problem is geometry, not spring tension.