How to Build AR 15 Lower

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Build AR 15 Lower

Building your AR-15 is one of the best and satisfying experiences. Also, you get to enjoy a customized gun that suits your needs. An AR-15 is made up of two main assemblies’, i.e., the upper and lower receiver. Building the lower, which is made up of other small parts, is not complicated. However, for some people, such as beginners in the AR-15 platform, it can be challenging.

This article has made it easier to build an AR-15 lower. It constitutes tools needed for the task, AR-15 lower parts, and a guide on bringing together all those parts to come up with a fully assembled AR-15 lower. Let’s get started!

Build AR 15 Lower
Build AR 15 Lower

Parts and Tools: Build AR-15 Lower

Your AR-15 lower cannot be complete if you do not have the right tools. These tools make the whole process easier and quicker. Here are common and readily available tools you must have with you:

  1. Roll Pin Punches
  2. Needle Nose Pliers
  3. Pivot Pin tool
  4. Punch set
  5. Roll Pin holder
  6. Armorer’s wrench
  7. Nylon/Brass Hammer
  8. Vise Block
  9. AR-15 Bench Block

You must also have the following parts to complete the build:

  1. Trigger Group
  2. Buffer Assembly
  3. Magazine Catch
  4. Trigger Guard
  5. Takedown pins
  6. Safety
  7. Grip
  8. Stock
  9. AR-15 Parts Kit.

That’s all you need. Below is how to do it.

A Guide on How to Build AR-15 Lower

This is a step by step guide on how to build an AR-15 lower receiver assembly. All the steps are simple and well outlined.  

Magazine Catch Assembly

  1. Start by placing the magazine catch into its slot in the lower receiver
  2. Hold it with your finger as you turn the lower to drop in the magazine release spring and the magazine button.
  3. Then press the magazine button and thread the magazine catch till it flushes with the other side.
  4. Ensure your installed magazine catch assembly functions.

Pivot pin

  1. Start by dropping the detent spring into its hole.
  2. Place Pivot Pin tool in the Pivot Pin’s slot
  3. The tool has a hole aligning with that other hole on the receiver where you placed your detent spring. Align it and then drop in the detent.
  4. Push the detent and turn the tool down
  5. Then push in the tool using the Pivot Pin till the detent clicks in place.

Bolt Catch Assembly

  1. Set your lower receiver on the vise block
  2. Then place roll pin on roll pill holder
  3. Align it on its hole and push in the roll pin.
  4. Proceed and put in the spring, plunger, and Bolt Catch. Ensure all those parts are well aligned and correctly installed.
  5. Remove the lower receiver from the vise block

Trigger Guard Assembly

  1. Press in the pin on the trigger guard and insert it on the side near the magazine wall.
  2. Then take your Nylon/Brass hammer and punch to drive in a roll pin and keep the Trigger Guard intact to the receiver.

Fire Control Group

  1. Set back your lower onto the vise block
  2. Start assembling your trigger group by placing adding the disconnector spring into the trigger. The fat side of the spring is the one that goes in.
  3. Then position your disconnector onto the spring
  4. Push a slave pin to hold all the parts together.
  5. Proceed and add a trigger sprig
  6. Drop that assembly into the lower receiver and align it with the trigger pin holes on the receiver.
  7. Drive-in your trigger pin to hold the assembly into your AR-15 lower receiver
  8. Now, assemble your hammer and hammer spring
  9. Then set it on the lower receiver with the legs of the hammer spring at the back of the receiver
  10. Align everything correctly before pushing in the hammer pin.

Buffer Tube Assembly & Stock

  1. Start by threading the castle nut onto the buffer tube and then add the castle nut.
  2. Thread the buffer tube into the lower receiver but do not go beyond the receiver’s buffer detent hole.
  3. Then drop in the buffer detent and spring in the hole mentioned above.
  4. Push in the buffer detent with one finger as you place the takedown pin on its slot.
  5. Also, add a detent and spring on the receiver’s back and align it with the end-plate.
  6. Push the end-plate towards the receiver and thread the castle nut to hold the end-plate in place.
  7. Use your Armorer’s wrench to torque down the buffer tube to about 35 pounds. That helps achieve a tighter fit between the buffer tube and the lower receiver.
  8. Then install your stock onto the buffer tube.
  9. Remove your lower receiver from the vise block
  10. Then insert a buffer spring and buffer into the buffer tube.

Safety and Grip

  1. Cock back the hammer and place your safety selector into the receiver keeping it in a “safe” position.
  2. Now, drop in your safety selector detent into its hole. You will have to position your AR-15 lower receiver upside down.
  3. Then align your pistol grip with the above spring and then press the grip towards the receiver.
  4. Drive-in your pistol grip screw into its hole to fix the pistol grip and the receiver together.
  5. Do not forget to add a pistol grip cap.

Now you have a fully built AR-15 lower receiver.


As you can see from the above guide, the process of building your AR-15 lower is not complicated. It only requires to allocate enough time for the build, purchase quality parts and tools and then follow the above steps.

However, you must note the laws and regulations within your respective state concerning building your own AR-15. All the best in your build!

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