There are many reasons why the semi-automatic AR-15 has remained the most popular of all civilian rifles. Applying the concept of modularity and modern lightweight materials to the AR-15, Eugene Stoner led the way for the development of all future sporting rifles. That’s made the AR-15 especially popular for those who want to add a customized touch to their rifles.
Let’s have a look at the factors that go into choosing a complete upper receiver and look at some more in detail.
Quick Comparison Chart of the Best AR-15 Complete Uppers
Aero Precision AR-15/M16 Assembled Upper Receiver
Bravo Company AR-15/M4 Flattop Upper Receiver Assembly
Armalite AR-15 A4 Flattop Receiver
Anderson Manufacturing - AR-15 Upper Receiver Assembly .300BLK; No BCG
Radical Firearms AR-15 Complete Upper Receiver Assembly, 10.5" Barrel, 5.56 NATO
Components of an Upper Receiver
The AR-15 is the two-piece type firearm consisting of two segments: the lower receiver and the upper assembly. The lower carries the firing mechanism and the magazine. The upper receiver contains the barrel, gas system, charging handle and the matching bolt carrier group.
For first-time AR-buyers, the simplest way to choose the correct equipment is to purchase a complete rifle from a trusted manufacturer. After a certain period of using and familiarization (read: shooting a few thousand rounds), you may decide to personalize and modify your Black Rifle to make it suit your tastes and use more. For example, an AR for target practice will need different components than a rifle intended for paramilitary operations or home defense.
Of course, you can always buy a dedicated rifle for any purpose you imagine, but it doesn’t seem like a practical or even less an economical solution. The AR-15 modularity enables us to easily swap out lowers and uppers in just seconds. For doing that, we have two possibilities. You can purchase a complete, pre-assembled AR-15 upper or a stripped upper receiver. The latter allows - or requires, depending on how you look at things - more customization.
The stripped upper is a single part - a solid piece of metal. A completed upper receiver will come in simple form with the forward assist button and ejection port door installed. The other variant is a full upper-half of an AR-15 rifle, and it is known as a "complete upper assembly", consisting of the complete upper receiver along with the barrel, gas block, handguard, charging handle, and possibly the bolt carrier group.
Benefits of an Upper
By choosing a complete upper receiver, you will prevent a lot of inconveniences. It also allows you a great deal of flexibility. When you purchase several upper receivers to go on just one AR-15 lower, you retain the comfort and spare the expense of having to replace your trigger, grip and other parts of a lower receiver. You can return your comfort level and only replace the original upper assembly. You can even have a different one customized for whatever role you’d like it to play.
Another benefit is less paperwork. Uppers are considered a simple addition to the gun. The lower receiver is the official, legal "gun" subject to the GCA (Gun Control Act of 1968) limitations. It is the part of the firearm which carries the serial number and is therefore subject to any federal or state laws regarding registration, background checks, and the like.
Things to Look for in an Upper
There are a plethora of complete upper assemblies available, varying in type, style, materials and contents in order to meet your needs for different kinds of shooting at different distances.
Over the past half-century, factory-grade AR-15 rifles have gone through an intensive development path reflected in varying renditions and iterations. For a civilian-build, the vital difference between A1, A2, A3, or A4 models comes down to whether the gun is a "flat top" or "carry handle" configuration?
The carry handle upper receivers feature a fixed "carry handle" on the top of the upper. This makes it perfect for your "Retro" or early AR-15 reproduction build. On the other hand the flat top has a Picatinny rail on the top of the upper. The latter is the most popular style of upper and provides more versatility, plentiful options and is generally more affordable.
Another fundamental that you will want to consider when selecting your upper are construction material. They are built from either sturdy aluminium or polymer. Generally aluminum models are forged from 7075 or 6061 processed with T6 heat treatment. The polymer material is not as tough as aluminium but is rather durable, lightweight and easy to produce.
The AR-15 receivers are constructed from one of three different styles manufacturing methods - billet, forged or cast-upper receivers. The cast-upper receivers are made through a "die casting” technique, ie pouring melted metal into a form. This receiver type is the lightest of the group but it offers the least amount of strength. Due to its questionable quality, it is not recommended for upgrading your Black Rifle.
The billet receiver is carved from a single billet block with a CNC lathe to the shape of an upper receiver. A forged upper receiver is created by "forging" (hammering) the hot aluminium into the standard form of the lower receiver. While the forged uppers are cheaper than billet, they are also the strongest and the most common type of receiver between all three styles.
Barrel selection is another essential part of the firearm. The standard AR platform can already fire over 90 calibers. If you make the decision to choose another caliber, and transforms our AR platform into a multiple-caliber systems, you probably need a dedicated barrel and a few other things. The AR upper assemblies are designed to easily switch between tiny .22 LR, all the way to the .50 Beowulf. But the most popular conversion is to the .30 caliber family, particularly the .300BLK, and it is usually preferred to other chamberings for hunting medium-to-large game.
Besides chambering, we also need to choose the entire length of the rifle. The gas system and barrel length bear the largest influence on this feature. There are three different gas system types available: rifle, mid-length, and carbine length. This dictates where the gas port is positioned on the barrel. Currently, the most-wanted combination is a 16″ barrel matched with a mid-length gas system. This combo provides a little more space for pressures to drop and therefore give a slightly softer shooting impulse.
Our next selection will cover mainstream complete upper assemblies that can be attached to your standard lower receiver to give you a taste of the AR’s versatility and adaptability.
Quick Take - The Best AR-15 Complete Upper Receivers
These are our recommendations for the best complete upper receivers for the AR-15:
Reviews of the Best AR-15 Complete Upper Receivers
Let’s have a look at the best options when you elect to upgrade with a complete upper.
Aero Precision is one of the few manufacturers that has made receivers for many big-brand rifles and it’s well-known name among AR aficionados who build their own AR-15s.
The Aero Precision AR-15/M16 Assembled upper receiver is a quality basic receiver with high overall marks for both machining and finish. This upper is constructed is made of 7075-T6 aluminum forged to M16/M4 specifications for .250” takedown/pivot pins. That makes it compatible with all mil-spec AR-15/M16 components.
The Aero Precision AR-15 Assembled Upper Receiver comes with a factory-installed the port door and forward assist and boasts M4 feedramps.
The AP upper is anodized. The black model has laser engraved T- marks; the Cerakote FDE model does not feature T-marks.
A drawback of this system is the lack of dry film lubrication on inside surfaces to help reduce wear.
Some users who would like to make a conversion to 9mm find this upper receiver inadequate. It requires a magwell adaptor due to the narrow rails.
As with all BCM products, this flattop upper receiver assembly is a quality addition to the market. Many AR fans and DIY enthusiasts consider Bravo Company the gold standard of modern AR-15s, making the best complete upper receivers. This is a top-tier brand that does not skimp anywhere It may cost a little bit more, but it offers a fully-assembled upper receiver with forward assist, and ejection port cover machined to correct mil-spec tolerances.
This Bravo receiver is topped with a mil-std rail featuring laser-engraved T-marks on the rail to enable easy removal and re-mounting of scope and other accessories.
This A3-style flattop upper is machined from forged 7075-T6 aluminum. It’s ready for use with barrels that use an M4 barrel extension. The Bravo upper can be used with any standard AR caliber build including 5.56mm NATO, .223 Rem, .223 Wylde, 300 BLK, or 6.8 SPC.
Due to its slightly-undersized inside diameter, the barrel extension may be too tight. The manufacturer recommends using a hair dryer to warm up the threaded bore of the receiver.
Eagle Arms and Armalite produce a famous line of sporting rifles called the M-15/E-15 as well as a dizzying selection of AR parts, assemblies and accessories.
ArmaLite’s upper receiver assembly is based on the A4 flattop receiver, and it comes in a package the same size as a generic M4 clone. It can be used with most common AR calibers like .22LR, 5.56 mm NATO, 223 Remington, .300 AAC Blackout, 223 Wylde, 5.56 mm NATO, and 6.8 mm Remington SPC. The Armalite AR-15 upper receiver assembly includes an M15 flattop upper with installed port door and forward assist.
This upper is made with forged 7075-T6 aluminum with a hard anodized coating and has a deep and even finish. It comes with a six-inches low-rise 1913 rail, ready to accept a detachable carry handle, optics or flip-up sights (BUIS).
The .300 Blackout is becoming increasingly popular for chambering and more available as dedicated rifles or complete uppers. The .300 Blackout conversion kits are great ways to quickly and conveniently build out or change an existing AR-15, so a lot of AR aficionados are now buying .300BLK upper receivers to add caliber flexibility to their Black Rifles.
The Anderson Manufacturing offers a .300 Blackout Complete Upper Receiver featuring a 16" barrel made of 4150 Chrome Moly Vanadium steel with a heavy barrel contour. The barrel features a phosphate/parkerized finish and sports a carbine-length gas system housed in the carbine-length A2 handguard. This particular Anderson upper receiver is built to mil-spec features longer and steeper M4 feed ramps.
The Anderson A3-style upper assembly does not include a bolt control group or charging handle. Nor does it have T-marks or a Picatinny rail. This AR-15 complete upper receiver is made of aircraft-grade forged 7075-T6 aluminum a hard anodized finish.
You may see a lot of complaints about the reliability of the .300 Blackout ammunition with a carbine gas tube. However, this problem can be solved by choosing the correct ammo, a heavier buffer and switching to a pistol-length gas tube.
We will note ta start our last proposal with a notice that this upper receiver comes with a barrel less than 16" in length. This may require special licensing as a short-barrel rifle. Be sure to check state and federal laws to make sure your build is permissible.
The Radical Firearms 10.5" Barreled Upper assembly utilizes a carbine-length gas system and comes complete with an ejection Port Door, forward Assist, 10.5-inch M4 Profile barrel, barrel nut and A2 flash hider. The package doesn’t include Charging Handle and BCG (Bolt Carrier Group).
The shorter carbine gas system has a bit harsher recoil and the faster cycle rate. To provide reliable feeding both the upper receiver and barrel extension feature the factory-machined M4 feed ramps.
The Radical mil-spec Upper Receiver is an inexpensive, flattop drop-in solution for any budget.
While this is an excellent upper assembly for the price, Radical Firearms also brings some quality-control issues like loose set screws on the gas block or uneven coating on the upper.
Similar to stripped upper receivers, complete assemblies offers a versatile platform for your AR-15 build. When choosing a complete upper assembly, please note the prices vary quite a bit, and a renowned brand is no guarantee of quality and flawless performance.
However you approach it, by following our suggestions in your search for the best AR-15 upper complete receiver for your needs, you’ll give your AR-15 rifle the new capabilities you’re looking for.