It’s common for the factory trigger in an AR-15 to be less than ideal. That doesn’t mean stock triggers are necessarily bad, but they’re not always the greatest. Factory setups are usually marketed as MIL-SPEC designs, which isn’t quite the shining recommendation some believe it to be. If you’ve considered replacing your AR-15’s trigger, odds are good you’ve fallen into the rabbit hole of aftermarket AR-15 triggers. Most are marketed as easy to install, and you might be wondering if that’s true. Today, we will walk you through the basics of drop-in AR-15 trigger installation and give you a few trigger tips along the way.
What’s a drop-in AR-15 trigger?
There are basically two types of triggers for the AR-15: standard triggers that come in pieces and drop-in models. The drop-in trigger design is often referred to as a “cassette trigger” because of the little metal cassette in which the working parts of the trigger are contained. The great thing about this design is that it’s a straightforward model for aftermarket upgrades. Of course, there are pros to standard triggers as well, such as the fact that they sometimes come with a variety of springs, so you can get the specific pull weight you want. That’s not to say there aren’t any adjustable cassette-style triggers, because there are, but the ability to change out springs is one plus of the standard design.
Another point in favor of a drop-in trigger is that they don’t get as dirty because the cassette surrounds and protects all those little parts. On the flip side, if something does go wrong, it’s far less likely you can somehow repair a drop-in trigger, whereas a standard trigger with all its easily accessible parts is far easier to fix for a broken piece. In all honesty, though, the pros of the drop-in trigger far outweigh the cons.
What tools do you need to install a trigger?
The tool list for the installation of a drop-in AR-15 trigger is short, and some parts are optional. At the most, you’ll need:
- Gunsmith hammer (one plastic end, one brass end)
- Screwdriver (typically a Phillips or flathead)
- Roll pin punch (the correct diameter for tapping out trigger pins)
- Allen key for the safety selector, depending on the design
- Allen key to adjust the trigger itself (should come with the trigger)
Step-by-Step Instructions
Now that you’ve gathered the necessary tools, let’s get started. Before you do anything, though, make sure your weapon is unloaded and the chamber is clear. Safety first!
Step One: Separate the upper receiver from the lower receiver
If you’re new to the AR-15, you might not realize how easy it is to access the working parts of your gun. Two takedown pins connect the upper and lower receivers. To remove the upper receiver from the lower receiver and install your trigger, simply push the takedown pins to the other side. Usually, you can remove the pins with your fingertips, but if you have stubborn pins, you might need to gently tap them out with a punch.
Note: Your BCG (bolt carrier group) needs to be in the forward, closed position before you separate the receivers. If it’s locked open, you’ll have a hard time taking the gun apart.
Step Two: Remove the pistol grip
The AR-15’s pistol grip is held in place with a single screw. You can access that screw through the base of the grip. Some pistol grips are left open at the bottom by design, while others have a hinged door. Simply turn the lower over, access the base of the grip, and you’ll see the head of the screw. You’ll need a screwdriver long enough to reach the screw head, and the type of screwdriver depends on the grip. Before unscrewing it, be aware there’s a tiny spring and detent at the top of the grip in a small hole connecting it to the lower. Don’t let the spring and detent fall out. Unscrew the screw and slowly remove the grip, grabbing the spring and detent and setting it all aside in a secure spot.
Step Three: Remove the safety
The safety removal process will depend on your specific gun. The two halves might screw together, or there might be a small set screw holding it in place, for which you’d need a compatible Allen key. Some safety selectors simply slide out in one piece (that’s the most likely design you’ll have installed on your factory AR-15). Whatever the design, you might need to wiggle it a bit to slide it free. Remove the safety selector and set it aside.
Step Four: Remove the existing trigger
Removing the trigger is the same process, whether it’s already a cassette-style trigger or a standard trigger. That said, if you want to reduce the risk of flying parts, there’s a specific process for disassembling the system if it’s a standard trigger.
Two trigger pins hold the trigger in place regardless of what kind it is. If your trigger is a cassette, simply push out the pins with your punch. However, if it’s a standard design, consider first pushing out the hammer pin (that’s the pin closest to the magazine well). This enables you to remove the hammer and hammer spring. Then, you can tap out the trigger pin that’s closer to the pistol grip and remove the rest.
The lower receiver should now be empty and ready for a new trigger. If there’s a tiny metal plate in the bottom of the receiver, go ahead and remove it because it was there for the proper fit of the trigger you just removed. Your new trigger might not need one.
Step Five: Install the new drop-in trigger
Take your new cassette-style AR-15 trigger and drop it in the receiver (if your receiver is filthy, clean it first). The trigger blade drops through the cutout and the cassette remains within the receiver itself. There are some exceptions to this with triggers that have removable trigger shoes, so you can select the type you prefer. In that case, you won’t want a trigger shoe on the post yet. You’ll simply put the empty post through the hole and place the trigger shoe afterward. This is typically done with a small screw to fasten the shoe in place.
At this point, you should be able to replace the trigger pins one at a time. Some trigger designs have set screws built into the cassette that are adjusted to align the cassette with the trigger pin holes or to make sure the cassette fits snugly in place. After installing more of these than I can count, I can safely say I’ve never had to adjust set screws prior to placing trigger pins. However, I have had to apply pressure on the cassette with one hand while placing the pin with the other.
If your trigger didn’t come with trigger pins—not all of them do—put the old pins back in. And if you’ve decided to place anti-walk trigger pins, which are great, follow the instructions for your specific model.
When the pins are back in place, adjust the two set screws to create the correct tension so the trigger cassette remains where you need it. Most cassette-style triggers have those screws and come with the correct-size Allen key.
Step Six: Replace the safety and pistol grip
To a point, you’re just reversing the steps you took to remove parts, but there are a few details worth mentioning.
When you install your safety selector, it will slide over the trigger, not under. This can sometimes take a little wiggling and adjusting, so be patient. When you go to replace the pistol grip, remember that the detent should be installed first with the spring behind it. Proper installation of these parts is necessary to ensure the trigger and safety work as they should. All parts should fit snugly into place and should function as they did before you replaced the trigger. To that end, running a dry-fire function test doesn’t hurt once you’ve put everything back together.
