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AR 15 - Upper Receivers


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AR-15 Upper Receivers Frequent Asked Questions

The AR-15 is a rifle comprised of two halves; the upper and lower mated together, each responsible for their own essential functions.

While the lower is the half of the rifle that’s considered the “firearm”, and therefore gets a lot of attention, the components that most largely determine the performance of the rifle reside with the upper.

The upper contains the bolt carrier group, and is the half of the AR-15 the barrel attaches to, so making the right selection of upper parts to match your desired performance is critical.

A significant advantage of the upper – unlike a lower receiver – is it's not considered a firearm by the Bureau of Alcohol, Tobacco, and Firearms.

This means you can purchase the upper and have it shipped right to your door, no FFL transfer and no paperwork. A shooter can assemble a variety of upper configurations and use all of them with the same lower. Meaning you only have "one" serialized firearm.

Perhaps you’d like a few options in alternate calibers, with different gas systems, different barrel lengths, or different optics.

Maybe you’d like a 5.56 NATO upper with iron sights for plinking and target shooting, and a suppressed 300 Blackout upper with a 1-6X variable zoom optic for hunting. Having two dedicated rifles is certainly an option, and if you want to get the absolute best performance from each specialized set-up, that is probably the way to go. But if you’re on a budget, or you just prefer to keep your trigger, stock, and all other factors consistent and have the flexibility of different calibers and set-ups, all you need is different assembled upper.

Hot Dog!

Many manufacturers offer a number of options when it comes to AR uppers, so what are the most important things to consider when choosing your next one? What makes a good upper receiver?

While there are many versions of the AR-15 upper , the most commonly available version on the market today is the flat-topped A4-style upper that does not feature a carry handle. So, what are uppers made of?

They come in a few different types of material and use different construction methods. It’s important to know the differences.

High tensile strength aluminum is the preferred construction material for AR-15 receivers, and it is generally accepted that 7075-T6 is the best aluminum for the task as it carries the MIL SPEC designation for the military’s M4 Carbine uppers and lowers. Some receivers you’ll find are made from 6061-T6 aluminum, which has less zinc in the alloy than 7075-T6.

This makes it easier to work with in the manufacturing process, but it is not as stress-resilient or as strong as 7075-T6 which can be as hard as steel. 6061-T6 aluminum will almost certainly be able to stand up to any demands you will be putting on your rifle, but understanding the differences is still better than being uninformed.

Receivers, both upper and lower, are made one of two ways; they will either be a forged receiver or a billet receiver.

A “billet” upper receiver is machined from a solid piece of bar stock aluminum. A CNC machine completes all the work, taking the solid block of material and trimming it down to the exact size and shape required.

This methodology treats the receivers somewhat like a sculpture, and it usually means there’s a large amount of customization that can be done on the receiver to make it more aesthetic and personal to the shooter.

There are a variety of reasons to consider various barrel lengths for your rifle.

Some applications, such as home defense, favor a shorter barrel length so that you can clear doors and hallways with ease. Professionals favor 10”-12” barrels for many close-quarters carbines, and you can replicate their performance with a similarly sized AR pistol. If you want a shorter AR, we recommend looking at a caliber like .300 Blackout, which excels in shorter barrel lengths.

For accuracy at further distances (or for hunting purposes), you’ll want the velocity and ballistic profile provided by a longer barrel. Many special purpose rifles will use an 18”-20” barrel to achieve a good balance of velocity and handling, though these rifles can still feel unwieldy in a hallway.

The most common barrel length for a 5.56 AR is 16 inches. With this length, you don’t need a tax stamp or a pistol brace, and you’re accurate out to 500 yards. It’s a comfortable middle-ground that does well in almost any setting.

A “forged” receiver uses large mechanical hammer to stamp out the rough shape of a receiver from heated aluminum. After the initial size and shape has been achieved, the receiver is then finished on a CNC machine.

It is generally agreed upon by metallurgists that, because of the compressive forces involved in the forging process, a forged receiver is stronger than a billet receiver. The shaping of the receiver under pressure causes the grain of the metal to follow the same shape as the receiver itself, providing for continuous grain characteristics in the overall product.

It is possible that you will encounter “cast” receivers from time to time as well. These are by far the lightest of any aluminum receivers, but also very much the weakest.

They are made by pouring liquid aluminum into a form, or cast, and letting it solidify. These are usually finished on CNC machines as well. While these are usually budget-friendly options and could be considered “good enough” for some applications, these are generally not made strong enough to be considered for use on a rifle you’d actually like to shoot often.

Quality AR parts manufacturers don’t produce these types of lowers, and we at Primary Arms don't carry any.

There are also a few special cases where companies will offer polymer uppers, usually reinforced with metal in key places.

These are far less common than lowers made of polymer which are rising in popularity and viability as a cost-effective option, and they are only a viable option for uppers if you are looking to build or convert an AR-15 in .223 Winchester or 5.56 NATO to an AR rifle that shoots strictly .22 LR ammo.

A polymer upper likely isn’t strong enough to be safely used with standard AR-15 loadings as the action of the rifle takes place in the upper.

Stripped uppers are the most affordable and offer the AR builder a chance to customize every aspect of the build with custom-selected parts. A stripped upper DOES NOT comes with a bolt or carrier, a barrel, a port cover, a parts kit, a charging handle, a gas system, a handguard. A stripped upper is the most base part when assembling your own upper receiver.

The assembled uppers include small parts such as the ejection port door and forward assist already installed on the upper receiver. this upper will not come with a barrel, charging handle, gas system, handguard, or BCG. A great place to start if you don't want to mess with tiny springs in the port cover, and forward assist.

Barreled upper assemblies come with the barrel already attached and generally include a drop in or free-floating handguard installed as well. These assemblies will also come with gas systems in place at a specified length. It is important to note, these barreled upper assemblies will not include a bolt carrier group or a charging handle, and those will have to be purchased separately.

If you’d rather purchase your upper with all the components included, a complete upper assembly is the best option. These assemblies come ready to be taken out of the box and mated with a complete lower receiver to form a complete rifle. Lots of owners will have several complete upper receivers, some with different length barrels, different calibers, or particular features, and have just one lower that accepts them all.

The forward assist button resides on the shooter’s right-hand-side of the assembly. This feature was added to Eugene Stoner’s original design during the period of time that was arguably the most tumultuous for the AR-15.

American soldiers overseas were seeing their rifles jam or fail to go fully into battery on a frequent basis, so the forward assist was added, along with a scored bolt carrier to allow the assist button to press the bolt forward manually. In the event that the extractor doesn’t clip around the rim of the casing, or the bolt head fails to lock completely into the barrel extension, the forward assist can be pressed or struck with the palm to attempt to properly engage the bolt carrier group.

Older ammunition had a high carbon content that led to frequent buildups inside the bolt carrier compartment and chamber. This caused the issues which made the forward assist necessary. Today, many will dispute the relevance of a forward assist, but the feature provides an additional level of control with negligible trade-offs.

Located on the same side as the forward assist, the ejection port allows for the spent casing in the chamber to be removed and flung out of the receiver by the extractor. This happens as the bolt carrier group slams rearward, cycling the firearm and stripping a new round into the chamber as it returns forward.

On most MIL-SPEC uppers, the ejection port will be coupled with an ejection port cover to protect the BCG and interior of the receiver from debris.

These can come already installed on a receiver or may need to be purchased separately. The MIL SPEC dust cover is made of aluminum, but many companies are offering custom dust covers for extra personalization and functionality.

One great example is the Strike Industries Enhanced Ultimate Dust Cover for standard AR and large frame rifles. These are made of polymer and feature a proprietary design that seals the ejection port more securely from dust and debris and are also built to attach and detach much easier than MIL SPEC dust covers.

The polymer construction allows the port to simply snap into place and function just the same as MIL SPEC covers that must be attached with a full-length pin that extends through the assembly. It is also completely resistant to rust and corrosion, and will never fade in color like metal dust covers often can.

If you are considering an upper that will be used with big bore AR-15 cartridges, such as .450 Bushmaster .458 SOCOM, or .50 Beowulf, then you should take note that the ejection port on a MIL SPEC upper will need to be slightly enlarged to accommodate the larger cartridge as it ejects. The standard size dust cover will still fit properly over top of an enlarged port.

Located just behind the ejection port, and in front of the forward assist on models that feature them, is the shell deflector, or brass bump. It’s a small piece of the unit's body that extends outward to intercept the rearward trajectory of a spent casing as it ejects through the ejection port and deflects the brass away from the shooter.

While it’s possible to operate a rifle without a brass bump – these are usually called slick- or slab-sided receivers depending on the manufacturer – shell deflectors do have the potential to improve the overall shooting experience, as the shooter doesn’t have to worry about hot brass ejecting back and towards his or her face.

While the Military stipulates that all upper receivers are hardcoat anodized in black, and this process has become standard industry practice for its durability and corrosion resistance, many manufacturers are offering their uppers with a variety of color options and coatings.

The anodization process can also be used to impart certain colors onto receivers, giving you some flexibility beyond the standard black finish. Even more colors like OD Green, Flat Dark Earth (FDE), Titanium Blue, Tungsten Grey, Burnt Bronze, Coyote Tan, or many others, can be applied to the receiver with topcoats like Cerakote or Duracoat.

These coatings go over top of the anodization and provide some additional protection and wear-resistance. A handful of manufacturers, like WMD Guns for example, will use a Nickel Boron coating, similar to the coatings that are popular on internal AR components, for a unique looking finish and excellent wear and corrosion resistance.

Keeping in mind that uppers come as either stripped, barreled, or complete assemblies, there is a considerable amount of price difference between types. The cheapest way to purchase an AR upper is to buy a stripped version and add the parts yourself. Barreled uppers will generally be more expensive, but not quite as expensive as complete uppers.

While many manufacturers will offer a variety of options, from stripped to complete, and the prices will vary, we have listed the popular brands we sell below and grouped by general price-points, from budget-friendly, to moderate, to high-end.

STRIPPED UPPER MANUFACTURERS:

BARRELED & COMPLETE UPPER MANUFACTURERS:

Our selection of AR upper receiver products includes AR stripped uppers, M4 uppers, complete upper receivers, skeletonized uppers, barreled upper receiver assemblies and more. Choose from products made by the world’s top manufacturers.

If you have any questions, don't hesitate to send us a message at info@primaryarms.com or call us at 713-344-9600.