AR-15s and AR-10s are accurate rifles right out of the box, but many shooters struggle to get the most accuracy because the heavy mil-spec trigger pull using standard grade parts. Normal trigger pull weight is in specification all the way to 8.5 pounds. They can also be rough and vary in pull during the operation. It’s much harder to shoot accurately with a heavy or gritty trigger. Fortunately there’s a multitude of replacement triggers available for AR-15 owners and most are simple to install—especially the self-contained, one-piece, drop-in triggers from Timney, CMC, Black Rain, and Patriot Ordnance Factory (POF). Here’s a quick tutorial for installing one yourself. In this instance, we’ve selected the POF single-stage 3.5# straight trigger that includes the KNS Precision fire control group pins, and we’ll be installing it in a Diamondback DB-10.
As always, visually verify the rifle is completely empty, let the bolt go forward on an empty chamber and place the selector in the safe position. Separate the upper and lower receivers, and keep the lower on your bench. There’s only a few tools necessary for this job: two 5/64″ hex keys, a screwdriver or hex key to remove the grip, punches to remove pins, and a non-marring hammer.
You will need to remove the pistol grip first. Look inside the grip and determine what is the correct tool needed to remove the bolt or screw. I’ve seen simple flat and Philip head screws and some that use a hex bolt.
Remove the screw holding the bolt in place and slowly remove the grip. There is a spring under pressure that holds the selector detent in place. As you remove the grip, be sure to keep you finger on the spring so it doesn’t launch across the room. Once the grip and spring are removed, the selector detent should fall out of the receiver. The selector can now be removed from the left side of the receiver by moving the selector in the middle of its range and pulled out. Keep all of these parts off to the side since you will be reusing them and they are easily lost.
Place the receiver in a receiver pin block, or on a handy roll of packing tape so when you tap out the trigger and hammer pins, the pins are contained in the block or center of the roll of tape. Using a brass or plastic punch and a light hammer (I used a small piece of wood), drive the pins through the receiver. It does not matter which direction you drive the pins out. I usually do the hammer pin first, then the trigger pin. The entire fire control group consisting of the hammer, hammer spring, trigger, trigger spring, disconnector and disconnector spring will come out of the receiver. You can reuse all of these parts for future builds.
The POF drop-in trigger has all of the parts necessary for the install including the self-contained trigger system, new threaded trigger pin, slotted hammer spring, two retainer and two small screws. Each screw has a small amount of thread locking compound to help keep the screws from backing out. Do not remove this compound.
While inspecting the new POF trigger, notice the two rubber rods attached to the bottom of the trigger unit. You will need to compress these rods a bit to install the KNS pins. The rubber puts pressure on the pins and helps hold them in place.
Drop the trigger unit into the receiver. Starting with the threaded trigger pin, put pressure on the trigger to compress the rubber compound to line up the receiver and trigger holes and put the pin through the holes. You may have to lightly tap the pin into place using a non-marring hammer (nylon) or a small block of wood. Either works fine and will not mar the receiver. The slotted hammer pin can be placed through the hole in the receiver and trigger unit. Both pins should be held in place by the pressure of the rubber pads in the base of the trigger unit.
The retainers have one slot and one hole in each of them. Place the slot over the hammer pin and rotate the pin until the hole lines up with the threaded hole in the trigger pin. Using a 5/64″ hex wrench, tighten the screw until it stops. Do the same with the other side. Using two 5/64″ hex wrenches, tighten the screws. The thread locking compound will make it necessary to use both wrenches at the same time to keep the other screw from rotating.
If it is your desire, now is the time to change out the grip or add an ambidextrous safety selector. Insert the safety selector into the receiver, then the detent pin. Here’s a tip: use some high quality thick grease on the detent to hold it in place in the receiver. It will keep it from falling out and make the operation of the selector much smoother. You can do the same with the safety selector detent spring with a dab on one end that you place in the grip. Work the grip into place and be careful not to bend or kink the spring. Tighten the grip bolt and you’re done with the installation of the trigger.
Perform a quick safety check on the trigger before putting the upper and lower receivers together. Pull the hammer back into the cocked position and place a finger in front of the trigger. Then, with the selector in the safe position, pull the trigger. The hammer should not fall. Do this a few times to make sure the safety is operating correctly. The selector may be worn or out of spec if the hammer falls during this test. Replace the safety selector if this happens, and then test again. Next, with the hammer in the cocked position, rotate the selector to the fire position and with your finger in front of the hammer, pull the trigger. The hammer should release and your finger should prevent the hammer from striking the frame. Do this a few times to see that the hammer and selector are working properly. Last test is for the disconnector. This insures safe semi-automatic operation. Cock the hammer and keep you finger on the hammer. Rotate the selector to the fire position. Pull the trigger, let the hammer go forward but do not release the trigger. While holding the trigger back, push the hammer back into the cock position. The hammer should catch the disconnector and sear, and the hammer should stay in the cocked position. Slowly release the trigger and listen for a click that signifies that the sear has re-engaged the hammer. The hammer should stay back when you remove your finger from the trigger.
If all is well and all safety checks are passed, unite the upper and lower receivers. Visually check to make sure the firearm is unloaded, and in a safe direction, perform the safety checks again. Now, you can head to the range and enjoy your new trigger. Your accuracy and split times should noticeably improve.