Assemble an AR-15 Lower Receiver

How to Assemble an AR-15 Lower Receiver

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Assemble an AR-15 Lower Receiver

One of the most incredible things about the AR-15s is that you can easily build one for yourself. However, if you are a beginner or new to the AR-15 platform, it can be scary since you might not have the skills to assemble all the parts. It’s not that complicated as it seems.

The AR-15 is divided into two major compartments, i.e., the lower and upper receiver that you must assemble for you to have a complete firearm. This guide will take you through how to assemble an AR-15 lower receiver.  Also, it has a list of all AR-15 lower parts that you will assemble and the tools needed for the task.

It’s an easy process once you are keen on each step. Depending on your availability, skills and parts assembling can take an hour, days, or weeks. Let’s get started.

AR-15 Parts Needed

Usually, the AR-15 lower receiver parts kit has about 30 parts. However, it’s exclusive of other vital parts such as the pistol grip, stock assembly, and the receiver itself. Depending on what you find more convenient, you can buy the kit or as individual parts if you need a more customized AR-15.

Here is the list of AR-15 lower receiver parts.

  1. Buffer Tube Assembly (Buffer Retainer, Buffer Retainer Spring, Buffer Spring, and Buffer Tube)
  2. AR-15 lower receiver (stripped)
  3. AR-15 stock
  4. A 30-round magazine
  5. AR-15 lower parts kit

There are different AR-15 lower parts kits available for your build. A standard kit comes with parts such as trigger &hammer springs, magazine catch & spring, magazine release button, bolt catch & spring, bolt catch plunger & roll pin, trigger & hammer, trigger guard, pivot pin & takedown pin, safety detent & detent spring, takedown/pivot pins & spring, safety selector, pistol grip, pistol screw & lock washer, etc.

However, the exact parts included in a kit depends on the manufacturers. Therefore, you might need to purchase a few of the individual parts or in smaller kits.

Tools Needed to Assemble an AR-15 Lower Receiver

Below are needed while assembling a lower:

  1. Brass/Nylon hammer
  2. Allen wrenches
  3. Armor’s wrench
  4. Roll Pin Punch set
  5. Needle Nose Pliers
  6. Vise with soft Jaws
  7. AR-15 Lower Vise Block

Steps on How to Assemble an AR-15 Lower Receiver

Step 1: Magazine Catch Assembly

  1. Drop in the magazine catch on it hole on the left side of the lower.
  2. Fix in the magazine catch spring on the right side and screw in the magazine button on top of it.
  3. Push in the magazine button inwards using a punch and turn the magazine catch clockwise till it clicks into place.
  4. You may do a test if it functions using your magazine.

Step 2: Bolt Catch Assembly

  1. Hold your roll pin using your pair of needle nose pliers and push it into its place (left side of the receiver) using a punch. However, drive it halfway.
  2. Then drop in the bolt catch spring into the holes below the roll pin and the plunger on top of it.
  3. Install the bolt catch as well while ensuring proper alignment.
  4. Then insert a pinch punch into the opposite side of the roll pin. It will help retain the bolt catch.
  5. Finally, use a Nylon/Brass hammer to drive down the roll pin completely.

Step 3: Pivot Pin Assembly

  1. Start by inserting the detent and spring into the lower receiver.
  2. Then compress it using a punch. However, hold it carefully as the detent can fly away. You can as well use a knife to hold it in place.
  3. Finish this step by pushing in the pivot pin until the detent clicks into position with the pivot pin.

Step 4: Trigger Guard Assembly

  1. Place your trigger guard into its slot on the lower receiver.
  2. Drive in the trigger guard screw. Use an Allen wrench.
  3. Finish the installation by inserting the trigger guard roll pin into its place. A nylon/brass hammer and a roll pin punch will help you handle this.

Step 5: Selector and Pistol Grip Assembly

  1. Drop in the safety selector into its hole on the left side of the receiver.
  2. Rotate it until it’s tight and ensure it points in the fire position.
  3. Turn your lower receiver upside down. It will allow you to install the grip.
  4. Fix in the selector detent into its hole on the receiver’s lower side where the grip will sit.
  5. Put the selector into the hole on the grip.
  6. Then correctly align the lower receiver and the pistol grip before pressing them together for a tight fit.
  7. Lastly, you will have to drive in the pistol grip screw to tighten the grip against the lower receiver using a flat-blade screwdriver. Also, insert the lock-washer.

Step 6: Trigger Group Assembly

  1. Set your AR-15 on the vise and utilize the vise block.
  2. In our case, we are using a pre-assembled trigger assembly.
  3. Drop in the trigger assembly with its springs pointing forward. Ensure it’s well-aligned in its place.
  4. Then place and align the disconnector on top of the trigger.
  5. If your trigger pinhole is clear after the alignment, push in the trigger pin. Use a nylon/brass hammer to drive in the pin to the other side.
  6. Now, install your hammer assembly into the receiver.
  7. Position the hammer assembly with the hammer spring ends, pointing the ends of the trigger spring.
  8. When the other hole on the receiver’s side is clear and the hammer properly aligned, proceed and install the hammer pin.
  9. The hammer pin is driven in as the trigger pin was fixed.

Step 7: Stock and Buffer Tube Assembly

  1. Start by inserting the takedown pin on its slot on the receiver.
  2. Then fix in the takedown pin detent followed by the takedown pin spring on the lower receiver’s rear.
  3. Now, it’s time to site the buffer tube assembly into the receiver.
  4. Thread the castle nut and end-plate onto the front side of the buffer tube.
  5. Procced and drop in the buffer retainer and buffer retainer spring on their slot on top of the lower receiver.
  6. Then slightly thread your buffer onto the receiver, then stop and hold the buffer retainer.
  7. Also, align the end-plate and push towards the receiver.
  8. Thread your castle nut until it tightly holds the end-plate. You can also use an Armorer’s wrench to tighten it further.
  9. Then put your buffer and buffer spring into the buffer tube. Ensure the buffer clicks into place past the detent.
  10. The very final stage entails the installation of an AR-15 collapsible stock on the buffer tube (you can use stock of your choice). Also, for the AR)-15 pistol version, you can use a brace.
  11. Align and push the stock into the buffer tube, holding the level downwards to allows its movement.

How to Build an AR-15 Gun?


The above steps are clear on how to assemble an AR-15 lower.  It’s a simple process when you have all the tools and AR-15 lower parts on your table. After you have assembled the lower, you then do a full assembly of the AR-15 upper to come up with a complete and functional firearm.

It’s that easy!

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