How to build an AR15 Rifle, Assembling a lower receiver

Building your own AR15 will help you to learn a lot about the function of this popular sporting rifle. A lot of people build an AR15 rifle so they can get exactly the type of rifle they want without wasting money buying parts they don’t need.

It is very fun to build an AR15 and enjoy shooting you’ve spent time putting together instead of just buying something someone else built. Some people are intimidated by the challenge of building their own rifle. However, once you see how easy the process it, they learn how much fun it can be.

The process of building an AR 15 is not very difficult and only requires a few basic tools.

Selecting the right parts

The first part of building an AR 15 is to select the right parts for your build project. You need to decide on the specific purpose for your rifle and select the components that will give you the results you want. Selecting the wrong parts will not give you good results in the finished product.

For my most recent AR 15 build, I decided to use an Anderson Manufacturing stripped lower receiver. I’ve used Anderson lowers before on other build projects and they work great. Anderson Manufacturing actually makes AR 15 lower receivers for many other companies who sell them at much higher prices.

There are certain parts I want to keep from a single company due to the machining tolerances. Each company has specifications they make their parts to comply with. If you use different components that interact with each other from different companies you may end up stacking tolerances that could cause potential issues. I will buy a lower parts kit from a single manufacturer to help avoid that problem.

My latest AR 15 build included a lower parts kit from CMMG. The company has a great reputation making quality firearms and firearm components. The trigger and hammer were polished in the right places to help improve the feel of the trigger press and help you remain accurate at the range.

Installing the Magazine Catch

The first component to in stall when you build an AR15 is the magazine catch due to other components making it harder to install later. The magazine catch will consist of three components, the catch, the spring and the release button.

Place the magazine catch into the lower receiver as shown in the video. While holding it with your finger, install the spring and button on the other side. Once you have rotated the release button down as far as you can go, take something to press it deeply into the frame and rotate the release itself until the threads are even with the button.

It is a good idea to use an empty magazine to test the magazine release to make sure it works properly. You should be able to insert the magazine and it should not release until you press the magazine release button.

Installing the Bolt Catch

The next component to install as part of building an AR15 is the bolt catch. This is the part of the rifle that will hold the bolt open once the last round is fired from the magazine.

There are several parts that are need for the bolt catch to function properly. There is a small spring and plunger that keeps the bolt catch depressed until the magazine is empty and pushes the bolt catch up. If the spring and plunger are not properly installed you could have malfunctions of the bolt locking open when there is still ammo on the magazine.

It is a good idea to get the bolt catch pin started into the receiver before putting the remaining parts into place. Use a good set of punches and something to protect the loser receiver from being damaged. Only start the pin into the frame; do not drive it all the way into position until the remaining components of the bolt catch are installed first. Yes, people have done that.

Using a small punch through the opposite opening in the loser receiver, hold the bolt catch into place and drive the pin home. The pin will push the punch out as it is driven into the receiver.

Installing the Trigger and Hammer

Selecting the right trigger and hammer for your AR 15 rifle build is where you can make or break your gun. Using a good fire control group is essential to having a good reliable and fun to shoot rifle. If the trigger is not crisp when you press the shot, you will not be as happy with your rifle build as you could be.

The trigger and hammer in the CMMG lower parts kit are polished on the right surfaces that will help make the trigger press very smooth and crisp.

Make sure you install the trigger spring and hammer spring in the proper orientation or it will not function properly. Once you have the springs installed, install the small spring for the disconnector into the trigger. This is a very important part that ensures your gun functions properly.

Drop the trigger group into the lower receiver and use a small punch to line everything up properly. Install the trigger pin into the receiver, using it to push the punch back out as the pin is pressed into place. Do not get to aggressive and damage the frame or the components.

It is also a good time to install the trigger guard into the receiver as well. Usually a small screw and a single pin is all that hold them into place.

Installing the takedown pins and buffer tube

The takedown pins hold the lower and upper receiver together and are held into place with small detents and springs. These are much easier to install them than most people think.

A lot of people find it very difficult to install the takedown pins into the lower receiver. The process is much easier if you follow the proper steps. There are special tools that are intended to help you get the pins and detents installed but a little care and planning will allow you to save your money to buy more guns and ammo.

The buffer tube and buffer retainer are also installed at the same time as the takedown pins. Install the castle nut onto the buffer tube and run it all the way back. Add a little grease to the threads to help protect them and make it screw together a bit easier. Slip the lower receiver end cap over the buffer tube and begin screwing the buffer tube into the receiver.

Run the buffer tube up close to the hole in the receiver where the buffer retaining pin and cap are to go. Install the rear takedown pin, detent and spring into the lower receiver. Hold the receiver up where the pin and spring will not fall out. Install the buffer retaining spring and cap into the receiver, press it down and rotate the buffer tube into position to hold the buffer retainer into place.

You should now be able to slip the end cap forward, compressing the detent spring and run down the castle nut onto the receiver. Tighten up the castle nut and stake the nut into place.

Installing the safety

It is critical the safety is installed properly whenever you build an AR15. You must ensure that it functions properly and keeps the hammer from going forward unless it is disengaged.

When you install the safety into the lower receiver you will need to cock the hammer back or you will not be able to install it. Make sure you keep your thumb in front of the hammer because you don’t want it going forward and slamming into the frame.

Once the safety selector is dropped into place, turn the receiver upside down and install the detent and detent spring as shown in the video. The detent spring will slip into a hole in the grip. Be sure the spring doesn’t get kinked as you install it.

Push the pistol grip into place and install the grip screw. Once everything is assembled, test the complete lower, making sure all the components work together properly and that nothing is binding

Taking the AR15 to the range

The best part of building your own AR 15 is being able to take it to the range and shoot it. When you build an AR15 you are always thinking about that first trip to the range with it.

It is a good idea to load a single round into the magazine for the first shot and then add a couple more once everything is shown to work properly. Make sure the bold locks back on the last round and there are no feeding issues.

When you build an AR15 you are making a lot of choices for parts that will end up becoming a functioning firearm to add to your collection. Make the right choice in parts and have fun putting them together.