5 Best Complete Uppers: A Complete Review and Guide

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Owning an AR-15 rifle comes with the need to understand its operating mechanism. One vital knowledge is on the upper receiver mechanism.  As you already know, the upper receiver is the lock-up between the barrel and bolt. It determines if your rifle is dependable and accurate or fires amidst conceivable frustrations. 

When building your AR-15, the upper receiver serves different purposes that are all important. These include general use, precision shooting, close-quarters combat, or home defense. 

This article will help you pick the best complete uppers in the market today.

A Review of Five Best AR-15 Upper Receivers

1. Aero Precision M4E1 16-inch 5.56 Mid-Length—Complete Upper Receiver—Atlas S-One Handguard

This Aero Precision M4E1 16-inch upper uses a mechanism similar to an M4 feed ramp to provide you with faster installations and support. T-marks on the receiver are laser engraved and even give accurate results following the design. 

It uses the same features as the Atlas S—One handguard. It means it has a ¾–inch gas block and 1-7—inch twists to give your rifle control as you fire. 

 The model comes in a black or tan finish. You can order the 12-15—inch handguard to better grip and control every shot you take. 


  • There is enough insulation from the outside body. This prevents vibrations from compromising your aim. 
  • It comes with a simple upper aim feature. 
  • Compatible with most muzzles and suppressors. 


  • Users complain of inconsistencies when using the .223 ammo. 
  • Some users find the design complicated to use. 

2. Aero Precision M4E1 Threaded 16-inch .223 Wylde—Complete Upper Receiver—Atlas S-One Handguard

The Aero Precision M4E1 Threaded 16-inch upper is outstanding and you can tell it from the long barrel. It has an E1 design that provides you with a flat surface resulting in better aim. But if you want, you can add sights to improve on your aim.

The stainless body of the .223 Wylde rifle barrel is an appealing feature that gives it a grim look. The design is flawless and ensures that bullets move unobscured from their trajectory when you fire. 

It comes with the Atlas S-One handguard feature, and this is an essential rifle part of this model. Because of the handguard, you will have a rear and front Picatinny rail setup. 

There are sling sockets to attach your sling to help you carry the rifle with relative ease. There is no central part of the rail, and this makes the upper receiver weigh less. 


  • The handle is comfortable for both right and left-handed users. 
  • Even movement of gases throughout the gun system
  • Versatile and compatible with most AR-15 rifles.


  • Users complain of the grip that comes with the receiver installation parts.
  • Requires regular cleaning

3. Aero Precision M4E1 Enhanced 10.5—inch 5.56 Barrel—Complete Upper Receiver

The Aero Precision M4E1 comes in three shades of colors to match your AR-15 model. Because of this, your AR-15 rifle will maintain its aesthetic appeal even if you are swapping the upper receiver parts. 

The sturdy build is because of the 7075 T651 aluminum body. You will enjoy the comfortable design as it’s compact and lightweight, weighing slightly under three pounds.

The gas block has few obstructions and provides easy handling for this low-profile rifle. It features a carbine length unit. 

It has a 1.78-inch diameter that supports muzzles and 1.5—inch suppressors. The M4 feed ramp links with the receiver within seconds as the installation process is fast and straightforward.  


  • Straightforward assembly and installation process
  • Handguard can be applied to the bottom of your rifle
  • Air moves all through the gun system to avoid obstructing the bullet when you fire. 


  • It doesn’t come with a charging handle
  • The muzzle brake isn’t pinned down or welded. 

4. M5E1 Enhanced Complete Upper—20-inch .308 CMV 5R Barrel

It’s a 20—inch model designed with an aluminum body that offers sturdy support. The unit uses an M4 feed ramp and a 1-10—inch twist position. The M5E1 Enhanced Complete Upper features a black barrel design that has a 15—inch handguard. 

There are slots for attaching your sling outside the receiver, which works exemplary if you attach it correctly. 

Because of the lower profile, the gas block offers you better shot placements. You can add a muzzle or suppressor at the front end if you wish. 


  • Compatible with many AR-15 .308 components
  • The gas tube runs along the entire barrel
  • Comfortable sling design and position


  • Needs outside sights to perform better
  • A heavy model compared to others is under review here. 

5. Aero Precision M4E1—Complete Upper 5.56—T ATLAS R-One Handguard

Nothing screams durability more than this model. Because of its carbine gas length, it’s suitable for home defense. While you can forge, it will only add more weight. 

The M4E1—Complete Upper 5.56—T ATLAS comes fully assembled, making installation take only a few minutes. However, its downside is that it comes without a charging handle and bolt carrier group. 

The muzzle brake lowers recoil to less than 50%, and this is a welcome addition. 


  • Durable and sturdy
  • Inclusive of an ATLAS R—One handguard
  • It uses a carbine-length gas tube
  • Inclusive of forward assist and port door. 


  • Users find it comparatively heavy
  • Not inclusive of charging handle and bolt carrier group making it an expensive model.

What are the Characteristics of a Quality AR-15 Upper Receiver

The complete upper receiver of the AR-15 consists of the following components:

  • Front sight
  • Gas system
  • Charging handle
  • Rail system/handguard
  • Slip ring
  • Dust Cover/ejection port
  • Bolt carrier group
  • Forward assist
  • And the barrel. 

The following six elements make the components great. 

1. Grade of Aluminum

The ArmaLite Rifle Company always uses the aircraft aluminum grade. There are two distinct categories of AR-15 aluminum grade. 

These are the 7075-T651 and 6061-T651. 

The former is preferred in modern AR-15 upper models because it has high tensile strength with little weight difference.  

2. Forged or Billet 

You can have either billet or forged uppers construction. Forged uppers are common and affordable, while billet constructions are more custom and have extra machining steps and finish. 

3. Barrel Length

AR-style rifles are modular because it enables the user to make changes on the lower and upper receivers with compatible pieces. The process is straightforward, and you can swap pieces in minutes using tools or not. You can change the traits of your rifle to suit different shooting modes.  

You can buy a ready-to-shoot AR-style rifle and upgrade it later by swapping lower and upper receiver components.  

The AR platform has a single lower (the only serialized part of the AR-15 rifle) that fits different upper receivers serving different purposes. 

If you are a beginner, you can start with a lower receiver and set up different uppers to complete your rifle. 

4. Complete or Stripped 

You can buy AR series rifles with complete upper receivers or stripped with only the bone stock in place. A complete upper receiver is ready to install the piece on the lower. The process is straightforward. 

The stripped option appeals to people who value custom rifles as they select each part themselves. The choices are determined by weight, price, purpose, and mil-spec. 

A complete AR-15 upper is a plug-and-play option that only needs sights and other optics as extra components. It becomes range-ready by simply marrying it with a lower. 

In terms of price, complete uppers are affordable because buying in bulk gets you discounts from gun makers. 

5. Piston or Gas system

The ArmaLite Rifles uses a gas system for cycling the action when you pull the trigger. The concept involves bleeding gas from a fired cartridge via a small port inside the barrel and into the gas block. Afterward, the gas is carried to the bolt along a gas tube running parallel to the barrel. This action works the bolt. 

It’s a method that has been consistently in service and reliable across many generations. But it isn’t among the cleanest options available. The gas system dispenses bullet particles and propellant gases back into the action. It can result in fouling, messing up the system each time you fire. 

6. Piston Guns

A new trend in AR-style rifles is using piston guns. The upside is that the operating rod cycles the bolt action into the receiver.

It pushes slightly hot gases and particulates inside the chamber. 

This results in a clean and reliable gun that you can use extensively without taking regular breaks to clean. 

Understanding the AR-15 Upper Receiver Assembly

The AR-15 upper receiver refers to the parts that formulate the bullet’s passage as it’s fired. The upper receiver assembly determines the projectile of the bullet, whether it will shoot even and in a straight line. 

When shooting the AR-15, it’s always vital to separate the gas from the bullet as you shoot. It keeps the rifle functional. 

The upper receiver design of the AR-15 allows the gas and the bullet to move out of the barrel separately. 

How Can I Assemble an AR-15 Upper Receiver?

Assuming you haven’t purchased a pre-assembled AR-15 upper receiver, you will have two options. Either you buy the parts of the upper receiver separately, or you buy an upper receiver kit. 

But if you are new to gun assembly, you should buy the upper receiver full kit. It’s because a kit will guarantee the sizes of the parts and that they all fit together easily. 

Before starting the assembly process, ensure that you have the proper tools readily available. These include an armor wrench, barrel nut wrench, bench vice, and a receiver block. 

Steps to Assemble an AR-15 Upper Receiver:

  • Start with installing the AR-15 forward assist. You will know that it’s lined up correctly if you can see the light from one end of the hole to the other. When you buy the upper receiver kit, the bare AR-15 comes pre-installed with the forward assist and ejection port door. 
  • AR-15 dust cover set up. The spring creates a challenge for beginners.
    The spring exerts pressure towards the dust cover. However, it can’t block the path as the rifle fires. The idea is to insert the retaining rod halfway when the dust cover is on, then position the spring using the retaining rod. 
  • Installation of the AR-15 barrel. Ensure that you screw the barrel in using enough torque. Anything less or more results in the inaccuracy of the rifle. Use the reaction for this process. Here the barrel nut couples the handguard and the barrel upper receiver. Remember not to over-torque. 
  • Installation of the gas tube. The gas tube is responsible for directing hot gas out of the barrel. It determines the energy that powers the action when you squeeze the trigger. 
  • End the process by installing the handguard. 


A complete upper receiver is an upgrade to your AR-15 rifle. It’s because you can alter and swap parts to fit your shooting purpose. You can get the most from your AR-15 rifle by choosing the best upper receivers in the market. 

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