How to Build an AR-15 Upper Assembly

Guide to putting together your AR-15 Upper Build Kits

Assembled Upper

Parts List for a Standard AR-15 Upper Assembly

  • Upper Receiver
  • Ejection Port Door Assembly
  • Forward Assist Assembly
  • Barrel
  • Barrel Nut
  • Gas Tube
  • Gas Block
  • Muzzle Device
  • Muzzle Device Crush Washer
  • Handguard
  • Bolt Carrier Group
  • Charging Handle
  • If you don't have the time to track down an entire upper assembly part by part then we have Upper Builds set up just for you in a ton of different calibers. These Upper Builds provide the option of an unassembled package for the ultimate DIY experience using this guide, or you can choose to have it put together by our team of Gun Builders. 
    Check out our Upper Builds HERE!

Recommended Tools

Upper Receiver Component Assembly

When building an AR-15 Upper, we’ve found it best to start with assembling the smaller components on the upper receiver itself such as the dust door and the forward assist if yours didn’t already come pre-installed.

Install Ejection Port Door

A standard AR-15 ejection port door installation (commonly referred to as a “Dust Door”) typically consists of the ejection port door itself, the ejection port cover pin, a c-clip for the cover pin, and the pin spring.

Dust Door Parts

- Press the small C-clip into the groove of the cover pin.

- Put the Ejection Port Door into place

- Slide the cover pin halfway into position

Installed Dust Door

- Place the spring into the hole, and continue pushing the rod through the door

- Twist the spring into the correct orientation. 

- Slide the pin through the spring and cover all the way to the other side and seat the back end of the cover pin into the upper receiver.

Install The Forward Assist

A standard AR-15 forward assist typically comes in an assembly consisting of the forward assist body, the spring, and the retaining pin.

- Put the Forward Assist body and spring into the hole into the upper receiver.

- The flat side of the forward assist body should be facing towards the inside of the upper.

- Compress the spring by pushing on the forward assist to align the roll pin hole with the slot in the forward assist.

- Press the roll pin into the small hole to keep the forward assist assembly in place using your hollow roll pin punch.

- Using a Master Bench Block like the one we carry from Real Avid is very helpful for this step. Having it placed in the block as shown in the photo helps keep the forward assist pressed in so you'll have your hands free to place the roll pin in. 

Roll Pin Tool

- The use of a hollow roll pin punch like the one from KAK Industries is incredibly helpful for holding the gas block and forward assist roll pins in place while getting them seated.

Installing your Barrel

Barrel Installation is much easier with the help of an upper receiver block in a vice. Make sure your upper receiver is properly secured on a vice block to avoid injury or damage to your project.


- Slide Barrel into the Upper Receiver, lining up the indexing pin with the slot.

barrel nut start

- Slide the Barrel Nut over the end of the barrel and get it started on the threads by hand. 

The use of grease on the threads of your barrel nut is recommended. If you choose to not use grease, the barrel nut can become much more difficult to remove in the future. AeroShell 64 Grease is a popular brand among professional and hobbyist gun builders.

Torque Barrel Nut

Barrel Nut Installation/Tightening

"Seasoning the Threads"

-  When tightening the barrel onto the upper receiver, you’ll need to initially tighten the barrel onto your upper receiver to its recommended torque specs. Recommended Torque specs range between 30 to 80 ft-lbs.  

- You’ll then need to loosen the barrel nut and retighten it again to the torque specs.  

- It is recommended to loosen and tighten at least 3 times to “season” the threads. This practice helps decrease the chances of the barrel nut coming loose over a long period of time.

Gas Tube and Gas Block Installation

Gas Tubes and Gas Block normally come in a set with the roll pin and set screws included.

Gas Tube and Gas Block

- If your gas tube and gas block aren’t already put together. You will need to align the roll pin holes together, with the gas port hole on the gas tube aligned to the hole in the gas block. This usually ends up with the gas block angling upwards when holding the gas block with the tube above it.

- Using a punch and a mallet, set the roll pin into the top hole of the gas block joining the gas tube and block together. Be sure that they line up correctly. 

- It can be difficult when installing the gas block roll pin using a mallet and punch, especially without the help of a block.

- After getting the roll pin started, An easy and popular alternative among gun buildings is using a pair of Knipex pliers or non-marring pliers to press the roll pin in flush and hold the gas block steady with your other hand. 

Press in Roll Pin

- Slide the gas block and gas tube over the end of the barrel all the way into place against the shelf on the barrel while guiding the end of the gas tube into the hole on the upper receiver.

- Make sure that the gas block is centered on the barrel so that the gas port on the barrel and the gas port on the gas block line up with each other.

Tighten Gas Block

- After Aligning the gas block and gas tube, use an allen key to tighten the two screws on the bottom of the gas block. 

- Many AR-15 Barrels come with a small locating dimple under the barrel where the gas block goes which makes it easier to align the gas block as you tighten it onto the barrel. 

Install your Muzzle Device and Crush Washer
Most Muzzle Devices come with the proper-sized crush washer included. Make sure your crush washer and muzzle device are compatible with the barrel and caliber you'll be using.

- Be sure that the crush washer is placed in the proper orientation. 

- A crush washer will have a bevel edge on one side angling outwards. Slide the crush washer over the end of the barrel with the bevel going towards the receiver. 

-Having the crush washer in the proper orientation is very important for keeping the muzzle device secured on the end of the barrel and allowing the muzzle device to be placed in the proper orientation.

Muzzle Device

- Start the Muzzle Device onto the threads by hand before using a wrench.

- Make sure that the cuts, holes, or grooves of the muzzle device you choose are in the correct orientation. Certain Muzzle Brakes and Compensators need to be timed correctly. Having the crush washer in the right orientation makes timing the muzzle device possible.

Tighten Muzzle Device

- With the help of a wrench, tighten the muzzle device against the crush washer until you get to the proper orientation you need. 

- Do not over-tighten your muzzle device. 

Install your Handguard

There are generally two types of free-float handguards:  

One style clamps to the barrel nut by tightening the bolts on the bottom of the handguard.  

 The other style of handguard normally comes with a barrel nut with threaded mounting holes allowing you to bolt the handguard directly into the barrel nut. This style requires the barrel nut to be timed correctly so that the handguard lines up properly with the upper receiver. Most handguards in this style come with a barrel nut and a number of shims/spacers to help everything line up more easily.

Install Handguard

- Slide the Handguard over the barrel.  

- Make sure handguard top rail lines up with the rails on the upper receiver

Tighten Handguard

- Tighten the Handguard onto the barrel nut using the torque specs recommended by the manufacturer of your handguard.

- Handguards commonly utilize torx head bolts.

Install your BCG and Charging Handle

Let's not forget your Bolt Carrier Group and Charging Handle. Even if you've got a pre-assembled upper receiver, removing and re-installing your Bolt Carrier Group and Charging Handle is an important step in cleaning and maintenance of your build. 

Insert Charging Handle

- Install your charging handle first by lining it up in the groove, this requires placing the charging handle into the main body of the upper receiver and sliding it into the channels for the tabs on the sides of the charging handle.

Install BCG

- Insert the BCG into the channel on the underside of the charging handle

Slide Everything in Place

- Slide the BCG and Charging Handle all the way in until they click into place

Aaaaaand.........You're All Set!

Assembled Upper

At this point, you'll have a functioning upper receiver in your arsenal! Congratulations!

What's Next?

Now that you've got a complete upper assembly there are still some finishing touches to get the most out of its capabilities. 

Choose your Optic or Sights

- Iron Sights or Flip-ups

- Red Dots and Optics

Choose your Upgrades and Accessories

- Handguard Grips (angled foregrips, vertical grips)

- Slings

- Bipods

- Lights/Lasers

What do you think? Leave a comment below to share your thoughts, input, suggestions, or tips and tricks for building your AR-15 Upper Assembly. 


Add Comment


james james

Date 10/3/2022

Well so far I have had no problem with Delta! The products are of good quality and the prices have been fair I like that the sale don't come all at once or I would miss a lot of them! Thanks

james james

Date 10/3/2022

Well so far I have had no problem with Delta! The products are of good quality and the prices have been fair I like that the sale don't come all at once or I would miss a lot of them! Thanks

0 Items