Building an AR-15 lower receiver for the first time could be nerve-wracking. This process needs a cautious and precise step-by-step walk-through. Therefore, you will need a helpful and informative guide to build your first rifle.
In this guide, we have gathered the best steps to follow if you want to know how to build an AR-15 lower.
Table of Contents
- 1 How to Build Your AR-15 Lower Receiver in 9 Easy Steps
- 1.1 1. Prepare Your Lower Receiver Parts Kit
- 1.2 2. Assemble the Magazine Catch
- 1.3 3. Assemble the Trigger Guard
- 1.4 4. Assemble the Bolt Catch
- 1.5 5. Insert the Front Takedown Pin
- 1.6 6. Assemble the Trigger
- 1.7 7. Assemble the Hammer
- 1.8 8. Assemble the Pistol Grip & Selector
- 1.9 9. Assemble the Buffer Tube
- 2 Some More Tips & Tricks
- 3 Wrapping Up - Building Your Own AR-15 Lower
How to Build Your AR-15 Lower Receiver in 9 Easy Steps
1. Prepare Your Lower Receiver Parts Kit
First, prepare your lower receiver parts/receivers kits. You may need some tools to build the parts, something like the punch set, charging handle, receiver extension, the fire control group, and c-clamp. You will also need an AR-15 firearms combo tool, which is best for installing the castle unit. A utility knife is needed to install the pivot pin detent.
2. Assemble the Magazine Catch
In the magazine catch assembly, install the magazine catcher into your lower to guide you to keep your lower receiver stable on the lower vice block. This way, your lower receivers will not touch the vice jaws.
First, insert the magazine catch into the hold found on the receiver’s left part. Place its magazine catch spring over the threaded portion from the right side of the receiver. Screw the button up to five turns. Using a 5/32” roll pin punch, depress the button into a clockwise turn until the end of the magazine catch button is flushed with the magazine button.
3. Assemble the Trigger Guard
First, attach the trigger guard assembly in front of the lower using the detent. Using a small block of wood, you need to support the trigger guard’s bottom flange. And then, get your drive pin punch and hammer/trigger pin, drive the roll pin into the trigger guard’s lower and rear. To check if you have successfully assembled the guard, depress the detent on the trigger guard in the trigger pin hole and pivot it to open.
4. Assemble the Bolt Catch
Place two layers of masking tape between the selector switch and the catch as your guide. Next, get the roll pins and punch them into the hole of the first hump using your 5/32” punch and hammer.
And then, install the bolt catch spring into the hole on the receiver’s left side. The catch plunger must be installed atop of the springs. Next, install the catch receiver, using the 3/32” punch to hold the catch assembly in place of the front hump. Lastly, drive the bolt catch roll pin until it forces the 3/32-inch punch out of the front hump.
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5. Insert the Front Takedown Pin
To insert the front AR-15 takedown pins, you will need to insert the takedown detent spring into the lower receiver’s small hole. Compress it using a razor blade or the blade of a box cutter knife. And lastly, slide the pins into the hole until the bottom of the low-profile gas block. Remember, the takedown pin detent must prevent the takedown pins from coming out of the barrel receiver.
6. Assemble the Trigger
To assemble the trigger, you need to place the trigger spring facing forward and under the trigger. Next, install a disconnector with the wider portion of the spring towards it. Push it in and position the disconnector atop the trigger.
Keep the trigger spring feet facing forward before inserting the trigger assembly into the lower. The trigger retaining pin must be inserted through the receiver, disconnector, and trigger.
7. Assemble the Hammer
To assemble the hammer, place the hammer spring onto the hammer while keeping its ends facing away from the strike face. Next, insert the hammer pins into the lower with its hammer spring feet pointing backward from the strike face. Using the 5/32” drive pin punch, retain the hammer in place while inserting the retaining pins into the receiver’s hammer pin hole.
8. Assemble the Pistol Grip & Selector
To assemble the selector and grip for precision shooting, you need to insert the safety selector using a hammer cocked back. Place it in the lower receiver’s left part, which is a “safe” position. And then, insert the selector detent’s pointed end towards the selector spring.
Push the detent into the bottom hole of the receiver where the grip was installed. Finally, compress the selector pivot detent spring with the grip. Install the pistol grip screw and lock washer inside the grip, and tighten them firmly into the receiver.
9. Assemble the Buffer Tube
In the AR-15 buffer assembly, insert the pin on the receiver’s right side. Use automotive grease to paint the grooves of the receiver. Then, use the head screwdriver to screw the castle nut into the buffer tube.
Then the buffer tube must be screwed into the lower receiver. It must touch the bolt catch buffer retainer to hold it in place. And then, insert the pointed part of the pin detent into the small hole of the parts/receivers’ backside.
Next, keep the pressure on the spring and detent using a razor blade or a box cutter knife. Go back to the backplate and move it back in place. Then, tighten the castle nut in place. You can now insert the buffer and buffer spring into the buffer tube in the barrel of your firearm. We suggest you look for an ideal barrel length for your AR-15 rifle.
Some More Tips & Tricks
Many builders may not require it, but we suggest using a vise and lower receiver vise block to build an AR-15 rifle lower. These tools would make the job easier, as it helps keep your lower build in place while you work.
Wrapping Up - Building Your Own AR-15 Lower
The lower receiver sits above the pistol grip, holds the trigger and hammer, and has a slot for the magazine.  Like the upper receiver, it is crucial to building an AR-15 rifle, so you will need extra care, as it may cause harm when twisting and inserting some of its parts. Nevertheless, building an AR-15 rifle lower isn’t truly impossible, even for some builders with no experience.