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How to Build An AR15 Upper Receiver: Easy 4-Step Guide

How to Build An AR15 Upper Receiver

Firearm assembly may not be a beloved hobby for many, but it’s certainly worth the experience!

I’ll be teaching how to build an AR-15 upper receiver, which is something every gun owner should try to learn about.

While there may be a lot of things to learn, tools to get, and parts to decide on, it’s all part of the fun of the build!

In the end, you’ll be glad you tried it. I know I am!

I must warn you that if you are a beginner, there will be a lot of confusing terms, so I suggest having a professional help you out.

God knows I needed the extra hand.

What Is an AR Upper Receiver?

For the newbies out there, all this technical information on an AR 15 upper receiver can be overwhelming to learn.

Before I start on the process of building one, you need to know what an AR 15’s upper receiver is and what it does.

Your rifle is formed by TWO main parts: your upper and lower receivers.

Your AR 15 upper receiver is made up of multiple parts that you will be building one by one in this guide.

The main purpose of an upper receiver is to house the bolt and connect it to the barrel.

It also helps determine weight, accuracy, and overall performance of the rifle.

The upper receiver group is FULLY CUSTOMIZABLE, depending on your intended use, budget, preference, and more.

While you can choose to buy one that is fully assembled, you can also build it from scratch.

Types of AR Uppers

There are 4 types of AR 15 uppers you can get.

The A1 is the original model for AR 15. These have a light profile barrel, forward assists, and fixed carry handle.

They also include a flip rear sight for elevation and come equipped with short and long-range apertures. They can be accurate up to 450 yards.

The A2 receiver is a step up from the A1. Its elevation can be adjusted up to 600 yards and can consider windage. 

I also have a full A2 sights removal guide if you’re interested.

The A3 has a flat top configuration and detachable carrying handle along with a rail and even high rise configuration.

Finally, the A4 uses M4 style feed ramps. These are the most common models available today.

What You’ll Need to Build an AR 15 Rifle Receiver:

What You'll Need

Before you start building your upper receiver for the AR 15, you must have the right tools with you.

Pay attention to the list in this guide and make sure you get everything that may currently be missing from your tools.


  1. Upper Receiver (stripped or fully assembled)
  2. Barrel
  3. Hand guard or rail
  4. Bolt Carrier Group or BCG
  5. Gas block
  6. Charging handle
  7. Gas tube


  1. Brass or nylon hammer
  2. Universal Bench Block
  3. Allen Wrenches
  4. Needle Nose Pliers
  5. Roll Pin Punch Set 
  6. Vise, w/ Soft Jaws 
  7. AR Lower Receiver Vise Block
  8. Standard Punch Set 
  9. Wheeler Torque Wrench 
  10. Sunex 97738 1/2-Inch Drive Jumbo Crowfoot Wrench
  11. AR Armorer’s Wrench
  12. Gun oil or grease
  13. Crush washer

Steps for Building an AR 15 Upper Receiver

Step 1: Install Your Forward Assist

Step 1

What You’ll Need:

  • Upper Receiver
  • Forward Assist (FA)
  • FA Spring
  • FA Roll Pin
  • Universal bench block
  • Armorer’s hammer
  • Standard punch or 3-1/2in. Roll pin punch (the latter is preferred)

You will only need to do this if you’re using a stripped upper receiver for your AR 15.

If you have one that is fully assembled, you can go straight to step 2 of this guide.

BEFORE YOU START THIS STEP: Put your forward assist on spring tension so you can drive your pin all the way into place.

Hopefully, when you release it, the upper receiver will capture the forward assist.

Afterward, follow the steps below:

  1. First, ensure the hook or tooth faces TOWARDS the receiver, with the hook part facing inside (away from you or towards the table).
  2. Next, put a piece of cloth or paper towel in the vice to avoid any marring then place the block with the upper receiver on here.
  3. Ensure the forward assist is already inserted in the spring. Now it’s time to carefully put the forward assist in the correct position.
  4. When you’ve got it, TAP the roll pin with a punch.
    • Make sure to press the forward assist in while you’re inserting the pin to ensure the raised part is caught by the pin and kept in place.
  5. Ask for assistance to hold the forward assist in place.
    • If you’re on your own, hold the forward assist in with your thumb while keeping the punch between your index and middle finger to hammer in the pin.
  6. Use the hammer to lightly tap on the pin far enough that it won’t come off your forward assist.
  7. Finally, finish everything with the punch.

Step 2: Install the AR 15 Dust Cover

Step 2

What You’ll Need:

  • Dust cover (a.k.a. ejection port cover)
  • Ejection cover rod
  • C-clip (a.k.a. snap ring)
  • Ejection port cover spring (a.k.a. hinge pin)
  • Needle nose pliers

The goal is to install the dust cover at the bottom right part of your AR 15 upper receiver.

The rod will go straight through your upper receiver with the help of the snap ring.

The clip or snap ring STOPS it from going further and is also held in place end with your handguard.

Then, the dust cover will be on the bottom part of the FA under spring tension.

Dust Cover Build

The FIRST and most irritating step here is installing your clip.

BEFORE YOU START: Take care not to lose them as they’re small and can easily fly across the room during your installation.

Better yet, work in a well-lit area and have a few spares on hand.

  1. Using your pliers, grab the clip on the side opposite the opening of the clip. Firmly (and I mean FIRMLY) grip your clip.
  2. Then, install it on the tiny notch you see right at the end of your ejection port cover rod
    • This is one of the most difficult parts of building rifle receivers, especially if it’s your first time
    • So BE PATIENT and try not to lose your clip in the process!
    • Better yet, get an ejection port that already has the clip installed so you can skip this part altogether.
  3. Now it’s time for you to install the dust cover onto your receiver.
    • Position the cover, then slide the first half of the rod in place before it comes out of the middle part of the cover.
  4. Get the spring. The spring or hinge pin’s long-arm should be facing the right (towards the rod), while the SHORT LEG will be on the LEFT.
    • When you put the spring into the dust cover, take the short leg and wrap it 180 degrees around so that the spring tension will hold the door open.
  5. You can use needle-nose pliers to help keep the spring in place.
    • Place the spring on the opening, push it through UNTIL it naturally captures and stays in place.
  6. Then, SLIDE THE ROD into and through the spring onto the other side of the dust cover.
  7. You may have to gently push the rod through until you hear a satisfying click.

How to Know if It’s Correctly Installed

To double-check if you’ve done a good job on your build:

  1. The long arm of the spring should correctly be in the RECESS and the short arm should just PEEK through the left portion, just above the dust cover.
  2. Then, close the cover and push the visible end of the rod to the right.
  3. The ejection port door should AUTOMATICALLY spring open if you correctly installed these parts.

Step 3: Installing Your Gas System and Barrel

Step 3

What You’ll Need:

  • Barrel
  • Barrel nut
  • Gas tube
  • Gas block
  • Rollpin for the gas block
  • Torque wrench
  • Armorer’s hammer
  • Bench block
  • 5/64 in. roll pin punch
  • Allen key (unless the manufacturer instructs you use another tool to secure the barrel nut)
  • Crowfoot wrench (depends on the design of the barrel nut) – If your nut has a different shape, the manufacturer typically includes the right wrench with it.
  • Gun grease

Gas Block and Gas Tube

  1. Place your gas block on your bench block.
  2. Insert the tube through the side, making sure that the bigger hole on your gas tube is facing down.
  3. The smaller holes on both the gas block and gas tube SHOULD BE ALIGNED.
    • The single pin will have to go through both of these parts (into the gas block, through the gas tube hole, and out through the other side of the block) to keep them in place.
  4. Install your roll pin into the block and through the gas tube. Use your punch and hammer to secure it through the gas tube.
    • It should be flush on both sides of the gas block. Set this aside for now.

Greasing Everything Up

  1. First, apply grease on your barrel nut (where the threaded portion is) and barrel extension.
    • You can do this using a cotton bud or just your finger.
  2. Be generous with the amount of grease you apply so that NOTHING BINDS when you install the barrel nut to the extension.
    • Double-check that you got grease in the threads of the barrel nut and extension.
  3. Just ensure you don’t go past the shoulder of your barrel extension.
  4. Now lightly grease the outside and inside of your AR 15 upper receiver extension.

Installing the Barrel

  1. Secure your barrel to your vice block with the threaded portion sticking out.
  2. Locate the small indexing point (small round indentation) on your barrel extension.
  3. Position it so it will meet with the notch inside your receiver extension.
  4. Push the barrel extension into the receiver extension UNTIL you hear a click and it sits in place.
  5. Wipe any excess grease.
  6. Thread on your barrel nut by inserting it through the barrel extension and into the exposed threading.
  7. Use the torque wrench to TWIST your barrel nut.
    • Do this until it reaches the right amount of torque specified by the manufacturer (between 40 and 50 foot-pounds).
  8. Use the metal shims the MANUFACTURER INCLUDED and insert them to push out the barrel nut from the other parts of the rifle receiver.
    • This will let you line up your gas block properly and aid with the gas tube alignment.

NOTE: There are some additional parts and steps you may need depending on the rifle barrel you chose.

If your barrel requires timing, you may find it difficult to get the right level with the torque wrench and align the gas blocks, no matter how much you twist the torque wrench.

Installing the Gas System

  1. Slide the gas block onto your barrel. Be careful to line up the gas tube with the gas port in your AR 15 upper receiver.
  2. Make sure everything is IN LINE (left to right) and that the gas block is pushed all the way up to the neck portion of your barrel. The gas tube should also still be in line.
  3. Tighten up the 2 set screws on the UNDERSIDE PORTION of your gas block with your Allen wrench or whatever tool the manufacturer has specified you use.

Step 4: Installing the Handguard, Muzzle Device, and Bolt Carrier Group

Step 4

What You’ll Need:

  • Handguard and mounting hardware
  • Muzzle device
  • Crush or peel washer
  • Bolt carrier group (BCG)
  • Charging handle
  • Partially completed AR upper receiver
  • Tool for installing handguard
  • Armorer’s or adjustable wrench

The size of your muzzle device will determine whether you need to install it BEFORE or AFTER the handguard.

A low-profile muzzle device can be installed AFTER the handguard.

But if you have a bigger/fatter model (e.g. cookie-cutter style), you will need to install that BEFORE your handguard.

Installing the Handguard

  1. Slide the handguard through the barrel of your partially completed AR 15 upper receiver.
  2. Make sure everything meets up in the middle.
    • Depending on the handguard you have, you will see tabs or any indentations to line everything up.
  3. Check the top portion (where the rails are located) to see if they are aligned.
    • Do the same thing with the tabs, which should go over the AR 15 upper receiver.
  4. Get the screws or mounting hardware that came with your handguard. Give the manufacturer’s instructions a read and follow them.
  5. Insert the hardware into the holes.
  6. Adjust the screws or mounting hardware to whatever torque the instructions require.
    • You will likely HEAR A CLICK or a sound when it’s achieved the proper amount of torque.

Installing the Muzzle Device

  1. Get the crush washer. The convex side, which looks like the inside of a bowl, should go towards the outside of your barrel.
  2. Put some grease on the inside threads of the device then put it on.
    • Depending on the muzzle devices you have, they may depend on certain timing.
  3. Simpler ones just have some grooves along the top.
    • You need to align the center groove with the grooves on the top of your AR 15 upper receiver.
  4. Use your adjustable wrench to tighten the muzzle and secure it in place.

Installing the Bolt Carrier Group

  1. Get your charging handle and LOCATE the tabs on its side.
    • These tabs should meet with the opening on the top of your AR upper receiver.
    • You’ll know it’s inside the opening or groove if it freely slides in and out without any trouble.
  2. Flip your AR upper receiver.
  3. Get your BCG and position it so that THE GAS KEY faces your right hand.
    • The partially completed AR 15 upper receiver parts SHOULD BE ON THE RIGHT of the BCG, flipped upside-down with the handle facing the BCG.
  4. Pull the bolt all the way out.
    • This ensures the pin inside the BCG is all the way out as well.
    • This is critical to successfully install the BCG.
  5. Now it’s time to clip your BCG UPSIDE DOWN and rest the gas key into the groove in the underside of the handle.
  6. Slide the bolt carrier group into the handle. Everything should easily slide into place.
  7. You’ll hear a click if it’s properly installed and your dust cover should have automatically popped open.
  8. Now you’ve got a complete upper receiver!

After this, you can install rifle sights or scopes, depending on what you want to use for your build.

You can also stick with the regular iron sight. It’s up to you to build an AR 15 you would love!

Advantages of Building Your Own AR 15 Upper Receiver


While this guide may not be for everyone, building an AR 15 upper receiver is just part of the fun of using a rifle, whether it be a AR 10 or AR 15.

I definitely learned some independence and patience trying to build an upper AND lower receiver on my own!

If you’re a hobbyist, it’s definitely worth it!

By allowing yourself to focus on this one thing, you can relax and take a break from your daily life.

Plus, it’s A LOT CHEAPER than buying one elsewhere. In the process, you’ll…

  • Learn more about your AR 15
  • Customize your upper receiver
  • Be more confident in the firearm you helped assemble

One thing you should remember is there are different parts to equip your AR receiver, depending on what purpose you intend to use it for.

This is meant to be a general guide so you can build an AR 15 receiver on your own.

The parts listed below depend on the kind of specific brand/model you choose and the build you’re aiming for.

If you want the best out of your receivers and build, aim to get gold-standard parts or parts favored among enthusiasts and professionals.

While these parts may cost more than other rifle receivers, they’ll work better and have added functionality (e.g. reducing barrel whip), and last longer in the end.

Frequently Asked Questions

How Much Does It Cost to Build an Upper Receiver?

On average, building an AR-15 upper receiver from scratch may cost around $700-$800, so I wouldn’t say it’s a budget-friendly activity.

However, this amount can vary depending on the materials.

If you can find a good deal on the parts and materials, it could be a lot more affordable.

If you factor in the cost of the lower receiver, it could set you back an additional $100-$300.

What Caliber Should I Build my AR In?

I’ve had a lot of success with the 22 Long Rifle.

It is a great choice for beginners as it has little recoil and high ammo availability, all at a low cost.

Other popular calibers include the 5.56 NATO, 6.5 Grendel, or .224 Valkyrie, all of which are options for hunting.

Do I Need to be a Gunsmith or Have a License to Build a Gun?

Nope! Anyone can build a gun as long as you have the proper supplies and experience.

Licensing only applies to dealers and sellers of firearms, so you can actually build one from the comfort of your own home!

If you plan to buy an AR-15, however, make sure it complies with state laws (or whichever location you are in).



The process of how to build an AR 15 upper receiver can be complicated and daunting, from the tools to the parts, and more.

That’s especially when it comes to delicate and small parts like the hinge pin or FA pin.

I highly recommend watching online videos and tutorials to see exactly what you need to do for the build.

Moreover, make sure to read the manufacturer’s instructions on how to build an AR 15 upper receiver.

Depending on the specific parts you choose, the exact steps and parts needed to build an AR 15 receiver may slightly vary.

I hope this general guide on how to build an AR 15 upper receiver helped!

FINAL TIP: For a related guide, you can also check out How to Build a Lower Receiver for Your AR 15.

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