Step by Step Guide: Assembling Your Custom AR Upper

Step by Step Guide: Assembling Your Custom AR Upper

Are you ready to take your AR-15 build to the next level? Assembling your custom AR upper can be a rewarding and educational experience. In this step-by-step guide, we'll walk you through the entire process of how to build an AR 15 upper assembly, from selecting the right components to putting it all together. Whether you're working with an FDE complete upper, a standard AR upper, or an AR-15 pistol upper kit, understanding the upper receiver and its parts is crucial. We'll cover the AR-15 upper parts names, provide tips on using an AR-15 upper kit, and even discuss how to build your own AR kit for a personalized touch. By the end of this guide, you'll know exactly how to assemble an AR-15 upper and feel confident in your ability to create a functional and reliable AR-15 complete upper. Let's get started!

Parts Needed for Complete AR15 Upper

Gathering all the required parts before assembling the AR upper is essential. Here’s a brief overview of each component you’ll need:

Stripped Upper Receiver

Anderson Stripped Upper Receiver

The stripped upper receiver is the foundation of your AR-15 upper assembly. It houses the bolt carrier group and provides attachment points for the barrel and handguard. Popular brands include Aero Precision and Anderson Manufacturing.


The barrel is a critical component that affects the accuracy and performance of your AR-15. Barrels come in various lengths and profiles, such as 16-inch for standard rifles or shorter barrels for AR-15 pistol kits. Brands like Ballistic Advantage and Faxon Firearms offer high-quality options.

Barrel Nut

The barrel nut secures the barrel to the upper receiver. It also provides a mounting point for the handguard. Ensure you have the correct tool to tighten the barrel nut according to the manufacturer’s specifications.


10" Premium AR-15 HandguardThe AR handguard protects your hands from the barrel's heat and offers mounting points for accessories. M-LOK and KeyMod are popular attachment systems. Options range from lightweight models by Magpul to robust designs by Midwest Industries.

Gas Tube

The gas tube directs gas from the barrel to the gas key on the bolt carrier group, cycling the action. Gas tubes come in different lengths depending on your barrel length and gas system (carbine, mid-length, or rifle).

Gas Block

Assembled .750 Low Profile Gas Block & Mid-Length Gas TubeThe gas block attaches to the barrel and channels gas into the gas tube. It can be adjustable or non-adjustable. Seekins Precision and Superlative Arms make reliable gas blocks.

Forward Assist Button and Spring

The forward assist button helps ensure the bolt is fully forward and locked. It’s not essential for all builds but adds an extra layer of reliability. Standard Mil-Spec forward assists are widely available.

Dust Cover

The dust cover protects the ejection port from debris when the rifle is unused. It automatically opens when the bolt carrier group cycles. Dust covers are typically included with upper receiver kits.

Hinge Pin

The hinge pin secures the dust cover to the upper receiver. It’s a small but essential component for correctly ensuring the dust cover functions.

Dust Cover Spring

The dust cover spring provides the tension needed for the dust cover to snap shut and stay closed. Make sure it’s installed correctly for proper operation.

Muzzle Device

AR-15 Muzzle devices include flash hiders, compensators, and muzzle brakes. They manage muzzle flash and recoil. Choose a device that fits your shooting needs, such as the A2 flash hider or the VG6 Precision Gamma.

Numerous Roll Pins

Roll pins secure various components in place. Please ensure you have the correct size pins for your parts and a roll pin punch set for installation.

Starting Steps: The Basics

Before you assemble your AR-15 upper, please ensure a clean, organized workspace and all the necessary tools. Follow these basic steps:

  1. Prepare the Upper Receiver: Install the forward assist and the dust cover on the stripped upper receiver. You can secure the forward assist with roll pins and a punch set.
  2. Install the Barrel: Place the barrel into the upper receiver and secure it with the barrel nut. Use a torque wrench to tighten the barrel nut according to the manufacturer’s specifications.
  3. Attach the Gas Block and Gas Tube: Slide the gas block onto the barrel, aligning it with the gas port. Insert the gas tube into the gas block and secure it with a roll pin. Ensure the gas tube is correctly aligned with the upper receiver.
  4. Install the Handguard: Slide it over the barrel and secure it to the nut. Depending on the handguard design, you may need to tighten screws or use a proprietary mounting system.
  5. Add the Muzzle Device: Thread the muzzle device onto the end of the barrel. You can use a crush washer or shims to ensure proper alignment and secure it with a wrench.

How to Install Each Part

Stripped Upper Receiver

  1. Forward Assist InstallForward Assist Installation:
    • Insert the forward assist spring into the forward assist.
    • Align the forward assist assembly with the hole in the upper receiver.
    • Use a roll pin punch to drive the roll pin through the receiver and forward assist assembly.
  2. Dust Cover InstallDust Cover Installation:
    • Place the dust cover in the open position.
    • Insert the hinge pin through the receiver and dust cover, along with the dust cover spring.
    • Ensure the spring is correctly positioned to provide tension.


  1. Barrel Installation:
    • Insert the barrel extension into the upper receiver.
    • Align the indexing pin on the barrel with the notch in the receiver.
    • Secure the barrel with the barrel nut, using a torque wrench to apply the recommended torque.

    Gas Block and Gas Tube

  1. Gas Tube InstallGas Block Installation:
    • Slide the gas block onto the barrel, aligning it with the gas port.
    • Insert the gas tube into the gas block.
    • Secure the gas block with set screws or a clamp, ensuring alignment with the receiver.
  2. Gas Tube Installation:
    • Insert the gas tube into the upper receiver, ensuring it aligns with the bolt carrier group.
    • Secure the gas tube with a rolling pin at the gas block.


  1. Handguard InstallHandguard Installation:
    • Install the barrel nut to the proper torque ranging from a minimum of 35lbs to no more than 80lbs
    • Slide the handguard onto the barrel, aligning it with the nut.
    • Secure the handguard using the provided screws or mounting system.

Muzzle Device

  1. Muzzle Device Installation:
    • Thread the muzzle device onto the barrel.
    • Use a crush washer or shims for proper alignment.
    • Tighten the muzzle device with an armor wrench, ensuring correct orientation.

Final Steps

Assembling the Complete Upper

Once all components are installed, it’s time to assemble the complete upper:

  1. Attach the Upper Receiver to the Lower Receiver:
    • Align the upper and lower receivers.
    • Insert the pivot and takedown pins to secure the receivers together.
  2. Install the Bolt Carrier Group and Charging Handle:
    • Insert the charging handle into the upper receiver.
    • Slide the bolt carrier group into the upper receiver, engaging with the charging handle.
  3. Test Functionality:
    • Ensure the bolt carrier group cycles smoothly.
    • Check the forward assist and dust cover for proper operation.
    • Perform a function check by manually cycling the action and ensuring the hammer drops when the trigger is pulled.

Testing the Assembly

To ensure your AR-15 upper assembly is functioning correctly, perform the following tests:

  1. Visual Inspection:
    • Check for proper alignment of all components.
    • Ensure all screws and pins are secure.
  2. Function Check:
    • Manually cycle the bolt carrier group to check for smooth operation.
    • Test the forward assist and dust cover.
    • Perform a dry fire to ensure the hammer drops.
  3. Range Test:
    • Take your assembled AR-15 to a shooting range.
    • Fire a few rounds to verify proper cycling and functionality.
    • Adjust the gas block if necessary to ensure reliable operation.

Following All State and Federal Laws

Adhering to all state and federal laws is crucial when assembling your AR-15 upper. Firearm regulations can vary significantly from one jurisdiction to another, so ensure you are fully informed about the legal requirements in your area. This includes understanding restrictions on barrel length, overall firearm configuration, and specific components like the forward assist or muzzle device. Please consult local laws and, if necessary, seek advice from a legal expert to ensure your AR-15 build is compliant and safe.


Assembling your custom AR upper can be a rewarding experience, allowing you to tailor your rifle to your specific needs and preferences. Following this step-by-step guide, you'll understand how to build an AR-15 upper assembly, from installing the forward assist and dust cover to attaching the barrel, gas block, and handguard. This guide ensures you comprehensively understand each component and its function. Please remember to follow all state and federal laws and regulations when building and testing your AR-15. Ensure safety and compliance at every step. For more detailed instructions on the entire rifle assembly, check out our other blog, "How to Assemble an AR 15: A Step-by-Step Guide." Happy building!

Jun 20th 2024 Black Rifle Depot Staff

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