The Basic Format.
It’s unlikely you’ll be installing a stock trigger in your rifle, but most aftermarket triggers still use the same essential parts in the same ways as the GI system. If you take your GI parts out for a clean and lube, reinstall them this away.
There are two pins—a trigger pin and a hammer pin. With exceptions usually encountered only in aftermarket sets, they are the same. Unless it’s Colt-brand, trigger and hammer pins are 0.154-inch diameter. Colt takes 0.173.
This is, or should be, a hand-done installation. One tool you do not need is a hammer. If a pin won’t fit into its receiver hole using finger pressure alone, either pin or hole needs a close look and perhaps an edge broken, or better alignment from you. Do not tap-hammer these pins! One tool that really helps is a correctly-sized (0.154 inch) punch used as an assembly slave, and mechanic-style gloves make the hammer’s installation less hurtful.
Test fit the pins. They should press into place through the receiver holes and the trigger and hammer should rotate freely on the pins.
Grease the pin holes on the hammer and trigger. This especially helps overcome the resistance from the hammer pin fitting over the J-spring within the hammer body.
Whatever you do, do not let the daggone hammer fall forward against the lower! The lower receiver can and will crack if the hammer hits it full-force. A well-positioned piece of leather or wood works when doing your tests and checks.
Place the trigger into the lower making sure the return spring stays in position. The disconnector spring is in its place. The tail of the trigger assembly goes under the safety bar, and the safety selector should be in the “FIRE” position.
Set the disconnector into its place and line up the holes. An assembly punch makes this easier. Push the punch in from left to right (because the pin comes in from right to left). Run the punch into the trigger but not into the channel where the disconnector sits and then position the disconnector, then push it through. The notch should be right over the disconnector spring. Push the disconnector down so its hole lines with the trigger pin hole.
Start the trigger pin from right to left, ungrooved end first. If you’re not using an assembly punch, use the trigger pin in the same way: push the pin into the trigger but not into the channel. Put the disconnector into place and push down on it to get alignment. Continue on until the pin enters the receiver hole on the left side of the receiver and comes to flush with its exterior surface. Done. Check that the trigger moves freely and the disconnector is free to rock to and fro. If it won’t, make sure its spring is seated.
The legs of the hammer spring should be pointing toward the rear of the receiver. Both legs of the hammer spring have to be on top of the trigger pin. One leg fits into the groove on the right side of the trigger pin to keep the trigger pin from slipping out. This is a strong spring. I use an assembly punch run through the left side of the receiver to position the hammer in place, and then the pin itself installs using the punch as a slave to guide it. To get the hammer in position, push down and somewhat forward on the hammer to compress the spring and lower its hole into alignment with the receiver holes. It will want to push back and up. The action that prevents it from winning this battle is a sort of pseudo-cocking force applied to the hammer with your fingers. The hammer is pushed down first and also then forward to position the pin hole. Keep pressure down on the hammer to get the pin fully through the left-side receiver hole.
Now that it’s all together, it’s a system and it all has to work.
The safety switch should only move from position to position when the hammer is cocked. When the hammer is forward, it should not go to the “SAFE” position.
Cock the hammer. Pull it back and push it down until it clicks into place. Rotate the switch to “SAFE” and pull the trigger. Pull it hard. Hammer should not fall. Rotate the switch to “FIRE.” Hammer should not fall. Pull the trigger and the hammer should fall.
Do not fire the rifle unless the disconnector is functioning.
The disconnector prevents the hammer from falling until the trigger is released forward enough to “reset” the sear and hammer hook or notch.
Cock the hammer and then release the hammer forward by pulling the trigger. Keeping the trigger held fully to the rear, cock the hammer again.
Now, just as slowly as you can, release the trigger forward. The hammer should “jump” up as it’s handed off from the disconnector to the trigger sear. I redo this check on an assembled rifle by letting the bolt carrier slam home to better duplicate firing. Then, of course, come range tests.
By Glen Zediker
The trigger pin installs from right to left (above), ungrooved end first. Glen uses an assembly punch. If you don’t, push the pin into the trigger but not into the channel. Put the disconnector into place and push down on it to get alignment. Continue on until the pin enters the receiver hole on the left side of the receiver and comes out flush. Done. Check the trigger moves freely and the disconnector is free to rock to and fro. If it won’t, make sure the disconnector spring is seated. The hammer spring (below) is strong. To get the hammer in position, push it down and somewhat forward to compress the spring and lower its hole into alignment with the receiver holes. It will want to push back and up. To prevent it from winning this battle, apply a sort of pseudo-cocking force to the hammer with your fingers. The hammer is pushed down first and also then forward to position the pin. Keep pressure down on the hammer to get the pin fully through the left-side receiver hole. An assembly punch run through the left side of the receiver to position the hammer in place really helps.
Here’s how the springs should look. The trigger-spring loops just snap fit into place over the bosses on the trigger. Note the orientation. The hammer spring installs in the same way. Orient the piece correctly and then snap one spring loop over one side and the other spring loop over the other side. The little feet are pointing, well, like little feet would point, and the square portion of the wire is under the sear bar.
OK, you’ve gotten your lower apart and this what you have. If you can reinstall all this, then most other available triggers will fit into place for you also. Don’t expect a good pull from a stock system. Engagement surface polish and lighter springs are about the only ways to make a standard trigger pull better. The pins are KNS-brand pins, correct and true. The same can be said for most pins supplied with aftermarket triggers, but a set of KNS will improve whatever a trigger pin set can improve. These pins always install from right to left, ungrooved end first. (Some aftermarket trigger systems and pins are an exception to this rule.)
Always (always) check for disconnector function (above). With the hammer fully forward and the trigger pulled fully to the rear, cock the hammer with the trigger held steady. Then, slowly, release the trigger forward. The hammer should “jump” up and hold when it’s handed off from the disconnector to the sear. Whatever you do, don’t let the hammer hit the receiver with full force. It will crack. Don’t confuse the bolt-catch-plunger spring (below, right) with the disconnector spring. They are just about the same size, but the disconnector spring has a larger end. This larger end goes into the recess located in the channel on the trigger body. Some GI triggers have two recesses. If so use the front hole. Put the spring into the recess and then push it fully home. Push it hard. You will feel it seat. Glen uses an assembly punch.
The preceding is a specially adapted excerpt from The Competitive AR15: Builders Guide, a book by Glen Zediker and Zediker Publishing. For more information, check out www.ZedikerPublishing.com or call (662) 473-6107.
200 S. Front St., Montezuma, IA 50171
KNS Precision, Inc.
112 Marschall Creek Rd.
Fredericksburg, TX 78624