How To Install An Ar15 Lower Parts Kit: A Step-by-step Guide

One of the most widely used semi-automatic rifles in the USA is the AR-15, and today you will find out how to install your lower parts kit for it.

Step-by-step instructions for installing the AR15 lower parts kit, including the trigger, hammer, safety selector, and other essential components, are provided in this article.

Before you start, ensure you have all the tools you need, such as a hammer, a set of punches, a vise, and a lower receiver vise block. Depending on the used kit, you may also need a torque wrench and thread locker.

Step 1 – Safety first

Ensure that the weapon is unloaded and you have a safe working area. Check the chamber and magazine to ensure there are no loaded rounds. Wear safety goggles and gloves for protection.

Disassemble the lower receiver by pushing out the takedown and pivot pins of the upper receiver. Next, remove the spring, buffer, and buffer tube. Finally, remove the grip and trigger guard from the lower receiver.

Step 2 – Install the magazine catch

For this step, you need the magazine catch, the release button for the magazine catch, and the magazine button spring.

First, you drop the magazine catch on the left of the receiver. Next, drop the spring and the release button for the magazine on top of it on the right side of the lower receiver.

Depress the spring behind the magazine release button with a punch. Then, screw the magazine catch button onto the threaded end. Tighten the button until it is snug but not too tight.

Step 3 – Install the fire safety selector

You will need a pistol grip and screw, a safety detector lever, and a detent and spring for this step.

Insert your safety selector in the lower receiver, drop the detent pointing upwards, and screw in the pistol grip but don’t overtighten it.

Step 4 – Install the trigger

The installation process may be different depending on your trigger type (drop-in or mil-spec). To place the drop-in trigger, all you have to do is drop in the trigger housing and install the locking pins meant to hold it in place in the trigger pocket.

The mil-spec trigger has more pieces that must be put together before installing it in the lower receiver.

You have the lower trigger part, which you insert in the lower receiver trigger pocket, then depress the disconnector and align the hole in the disconnector with the hole you see in the trigger bar. Then, install the hammer and its spring and use a punch to stick the hammer in the remaining hole of the lower receiver. Then, replace it with a pin from the opposite side.

Step 5 – Install the bolt catch

You need a bolt catch lever, a plunger, a spring, and a rolling pin. This can be the trickiest part. You start by dropping the spring in the bolt catch hole with a plunger on top. Partially hammer the roll pin on the side, leaving room for the bolt catch lever.

Depress the bolt catch lever down and align the hole with the lower receiver pinhole. Hammer the roll pin in until it is flush with the edge of the receiver hole.

Step 6 – Install the buffer system

You will need the mil-spec buffer tube, a buffer spring, a buffer weight, an end plate, a castle nut, a detent, and a spring for the takedown pin to install the buffer kit.

First, slide the rear takedown through the holes and ensure it’s seated. Drop the detent and spring in the small hole in the rear face of the lower receiver. Smash the spring down to hold it into place with the end plate using a thin flathead screwdriver.

Use the castle nut to tighten down on the end plate using pressure. You can crank it down with an armorer’s wrench if you need it to stay in place. You can pin it in place forever by taking a punch and hammering it downwards on the nut.

Step 7 – Install the takedown pins

After adding the rear takedown pin, you can move to the front takedown pin. This time you put in the spring first and then add the detent. Use a thin flat screwdriver to make the job easier.

Step 8 – Install the trigger guard

AR 15 forged lower receivers need a trigger guard you usually purchase separately. The good part is that this piece is easy to install. All you need is the part and a screwdriver. You screw in the screws on the right and left of the sight and set it, and that’s it.

Step 9 – Check the AR 15 functionality

After installing all the pieces, check the functionality of the AR 15. That means checking the trigger, safety selector, and magazine catch.

Ensure that the trigger can reset and that the safety selector movement is smooth when moving from the safe to the firing position. Test the magazine hatch button to ensure it engages and releases the magazine properly.

Step 10 – Final maintenance

Before using your AR 15, be sure to perform a final check. Ensure all the screws are in place and tightened with the pins to the manufacturer’s specifications.

You can apply a thread locker to the screws and pins to prevent them from loosening over time. It can happen when the gun recoils and vibrates. The final step is to clean and lubricate the lower receiver and the trigger. Ensure the pieces are well lubricated before using them to reduce friction and ensure smooth operation.


Installing the AR 15 lower parts kit is a relatively straightforward process when you have the proper knowledge and tools at your disposal.

Remember that safety is paramount when handling a firearm and that you should always refer to the manufacturer’s instructions before making any changes or installations.

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