- Receivers Explained
Not All Receivers Are Equal
When selecting a receiver set for your build, there are many options available to you in our wonderful land of capitalism. While features abound on any type, the first decision you will have to make is whether to go with billet or forged receivers.
The material that most AR receivers are made from is 7075 aluminum, which is preferred over 6061 aluminum due to its strength, this is especially true for the upper receiver. AR receivers come in many styles and flavors, while the materials they are produced from can vary from polymers to exotic metals. For the purposes of this post, we’ll be focusing on the more standardized 7075 aluminum. The difference between billet and forged receivers is in how they are processed and machined.
Color options are also available, including Wilson Combat's Armor Tuff, VLTOR's Gun Kote and custom Cerakote coatings from Strong-Side Tactical.
A billet receiver starts out as a block of a material and isn’t anything special other than being a rectangular block of aluminum (also called 'stock'). To make a billet block into an AR receiver, the block is placed into a milling machine and material is removed until it begins to take the desired shape. A good CNC machine should be able to hold a much tighter tolerance than Mil-Spec, usually around +/- .005" vs +/- .01". Since the machinist is starting with a solid block of material, creativity can be injected into the process to make unique designs, or even add features. Popular features include integrated trigger guards for added strength and extra room for gloves, forward assist delete for a smooth look, flared magwells, ambidextrous compatibility, precision bolt carrier raceways, set screws instead of roll pins and different shapes on the front face of the magwell.
Most billet receivers have thicker walls, which results in a stiffer structure to resist the forces applied to them. This added strength does come at the cost of added weight, even after material is strategically removed. The extra weight is minimal and centered on the rifle, so in many cases this is not an issue. A majority of billet lower receivers feature an integrated trigger guard, which can help add to the stiffness of the lower itself. When comparing the weight of a forged to billet receiver, make sure to include the same parts on each receiver. For instance, if the billet receiver you're comparing has an integrated trigger guard, you need to take the weight of a Mil-Spec trigger guard and add it to the forged receiver.
There are also lightweight receiver sets that have had material removed with the end goal being a reduced weight, usually at the expense of being less rigid. Some have gone to the extreme of skeletonized cuts that go all the way through the receiver. We would urge you to consider the environments you will be encountering. Here in Colorado, most of our matches take place in a sandy, silty environment where high winds are common. Having course sand blowing inside your rifle can end a match and could cause damage to the receivers, trigger and bolt carrier group.
The added mass of most billet receiver sets are a plus for long, heavy barrels or hot cartridges like the 6.5 Grendel. The additional weight of heavy barrels, bipods, lights and other gear can put stress on the walls of the upper receiver. Pair this weight with a hot cartridge using a suppressor and you've got much more pressure on the upper receiver than it was intended to take.
Billet receivers can also be easier to assemble, as many of them don't require roll pins. Instead of roll pins, a majority of billet lower receivers will use set screw pins that don't require a hammer and punch or a press to install. Another nice feature are manufacturers that thread the rear take down detent hole, making the installation of the buffer tube a breeze.
Billet receivers are not considered to be Mil-Spec because the manufacturing process, materials and dimensions can vary from the military call-outs. Due to the added thickness and custom designs, some Mil-Spec style parts may have fitment issues. However, most manufacturers of billet receivers pay special attention to not lose compatibility with certain parts. Hand guards that use indexing tabs may need to be modified for proper fit.
*Billet uppers use the straight pin dust cover rods
To Assist, or Not Assist
Many billet upper receivers (and some forged) don't have a forward assist and the value of an assist is really up to the customer. A large majority of people don't feel the need for this feature (us included) because the last thing you want to do in a malfunction is jam a bad round into the chamber. Most people are trained to get a fresh round into the chamber instead of driving a questionable round with force. The forward assist can be an asset if you're in a very dirty environment like a jungle or desert, as debris can build up and cause the bolt to not go into battery. Another use for a forward assist is if you're hunting with a suppressor and don't want to walk around with a live round in the chamber. When you're ready to take aim, you can slowly cycle a round into the chamber and let the bolt carrier down slowly. If it doesn't go all the way into battery, you can use the forward assist to drive it the rest of the way home.
A forged receiver also begins life as a piece of aluminum, but is formed by being hammered/compressed into a die shape that is generally close to that of the finished product. The process of the compression forging adds strength to the material for a better foundation. From there, the machinist removes small amounts of material with a CNC machine to bring the specifications down to their final size, then completes the details such as broaching the mag-well and drilling holes for trigger pins, safeties, etc… Due to the process of forging, there can be small indentations transferred to the receivers from the compression.
Forged receivers have been the standard for decades and continues to be the most popular way to manufacture receivers for the AR15 platform. They are also the most economic chassis for a rifle, due to the small amount of machining needed when compared to a billet receiver. Forged receivers are also lighter than their billet counterparts in most cases. All forged receivers will look almost identical, with the exception of small design features from the manufacturer and the placement of the roll marks.
Quality varies from one forger to the next, but most are relatively the same. The end result is usually dependent upon who is doing the finish milling on the receivers. Proper tooling, machining, tolerances and the finishing solutions eventually dictate the quality of the piece. Companies like Wilson Combat maintain tolerances that are beyond Mil-Spec (+/- .005" vs +/- .01") so that the fit and finish is as close to perfect as possible. It is recommended to source your receivers from reputable companies where quality is closely watched.
*Forged lowers require a port door rod with an enlarged end or a C clip.
The different forgings have markings to distinguish them from one another. These forging marks can range from simple letters or shapes to small icons like a key hole. These forging marks are usually found behind the ejection port on an upper receiver and on the right side of a lower receiver, just in front of the grip. Forge markings are much more common on upper receivers, as there are many forged lowers that do not have any kind of forge marking. Billet receivers don't have these marks, unless a company decided to machine them in to for a cosmetic touch.
Thick-Wall Forged Overview
VLTOR Weapon Systems has their own version of a forged upper receiver, which is referred to as the "thick/heavy wall forged" upper receiver. The MUR (Modular Upper Receiver) line of receivers are forged uppers that are similar to other Mil-Spec receivers, but are made with thicker walls for a more rigid structure. A rigid receiver will resist torquing and twisting during the cycling process, resulting in a more accurate rifle. Going beyond Mil-Spec, VLTOR also incorporates many processes to increase the strength even further, including heat treating, cryogenic treating, aging and is stress relieved. The inner lining of the receiver is also coated with a dry film lube to reduce friction on the bolt carrier group. Unlike standard Mil-Spec forged uppers, the VLTOR is available in a model with a forward assist (MUR-1A) and without a forward assist (MUR-1S), both include an installed dust cover.
Forged vs Billet vs Cast vs Polymer
- Since a forged receiver is very close to its final dimensions when it comes out of the forge, there isn’t a lot of room for customization and they are all about the same, no matter what company machines them. Some companies have manufactured their own dies, but they still carry a very similar style. Where manufacturers can offer some proprietary features is in their finishes, tooling quality, weight/material removal or their engraving and roll marks. Otherwise, they are all extremely similar with a few exceptions like the VLTOR receivers.
- The forging process gives the aluminum a continuous grain characteristic, which results in the receiver becoming stronger than a cast or billet part of the same thickness. This forging process can also have slight surface imperfections such as small divots. The forged receiver has been the standard for decades and is the most popular type of receiver.
- Billet receivers can be made (and usually are) with thicker walls and unique designs because the machinist is starting with a raw block of material. Thicker walls help to minimize flexing in the receivers, making for a more rigid platform. Most of the time, this added strength comes with added weight.
- Historically, the general consensus has been that billet offers more precision. Where billet has an advantage is when the lower and upper receivers are milled/fit as a “matched set”. These sets allow a tighter fit when paired together because they are hand fit at the factory and stay together during the whole process of manufacturing. A tighter fit can help increase shot to shot accuracy at longer ranges.
- Billet receivers typically cost more than forged because of the extra machining time or additional feature sets. We recommend primarily considering the different features that are offered and then look at the aesthetics. The price increase is easier to justify if you're getting better use out of unique features, instead of just paying for a unique look.
- In our opinion, cast receivers (especially uppers) should be avoided like Ebola. Cast receivers don't have the strength or durability to stand up to the abuse we put our rifles through during 3 gun matches, patrol work or military purposes. The price increase from a cast receiver to a forged receiver is minimal, so we highly recommend saving a few extra bucks and staying away from any kind of cast receivers.
- Polymer receivers have seen an increase in popularity over the last few years. Many manufacturers incorporate polymer receivers into their .22LR rifles to shave weight and reduce costs. While there are some good quality polymer receivers on the market, we feel that it's just not a durable enough of a material to withstand the abuse that someone might put it through. For rifles that will see extremely light use, a polymer lower would probably be just fine. Due to the pressures and wear characteristics, a polymer upper receiver is not recommended for any caliber other than a .22LR.
For all intents and purposes, billet receivers are more refined and every manufacturer offers some sort of proprietary aesthetics or features to set them apart. While billet may look “cooler”, add features or give your rifle a more refined feel, the justification for the price delta is entirely up to the end consumer. Inherently, AR style rifles will function the same whether they are built on billet or forged receivers. Both will have some common feature sets like M4 feed ramps and fire control markings. Similarly, a Timex and a Rolex will provide accurate timekeeping; one just does it with more precision, finesse, durability and style.