Brownells BRN-180 Upper Receiver Group

Most of us know about the Eugene Stoner's AR-10 and the subsequent creation of the M16 rifle, but do you know about the other ArmaLite rifle – the AR-18? Well, Brownells has replicated (and improved) it with its AR-180 upper receiver group: the BRN 180.

Brownells BRN-180 Upper Receiver Group
Photo by Mark Fingar

After designing the AR-­10 and witnessing its descendants’ successful adoption by the U.S. military, ArmaLite and Eugene Stoner decided to take another run at the large-frame automatic rifle. Work began on the AR-­16.

With the patent for direct-­impingement operation sold to Colt, ArmaLite and Stoner had to design a new system and they decided on a piston-­operated rifle. Stoner and team also wanted to simplify the manufacturing process, so they placed emphasis on using sheet metal instead of forgings or billet. This decision put them on the road that would eventually lead to the AR-­180 and to Brownells’ new BRN-­180.

Brownells-BRN-180-1
Photo by Mark Fingar. The original AR-180 had a sheet-metal receiver and polymer handguards. The BRN-180 has an aluminum billet receiver and an extruded aluminum handguard. Both are significant improvements.

Sheetmetal Was Once Sexy

One of the big takeaways from World War II was that really good military small arms could be made from sheet metal and automatic screw machine parts. The Germans proved that such feats were capable with the MP40 submachine gun and the Sturmgewehr StG 44 rifle, both highly regarded and heavily used in the big war.

Both the American and the Soviets took note of the successful implementation of sheet metal fabrication into military small arms and both proceeded to design weapons using this new technique. The Soviets first attempt was the AK-­47, but they were unsuccessful and had to resort to slower and more proven milled billet to get the rifle into production. Years later, they figured out sheet metal and the AKM was born.


The American market was much slower to move towards sheet metal firearms. The commercial market is where American manufacturers make their money and nobody needed to be reminded the commercial market wasn’t in the mood for cheap looking sheet metal. At least not in the 1940s and ’50s.


Stoner’s first use of sheet metal came in 1961 when he unveiled the AR-­16. He pitched the idea to the Army Tank Corps because it had a side-­folding stock, was inexpensive to make, and could fire rifle grenades without modification. It weighed 8.75 pounds, had a 15-­inch barrel and cost about $50 to make. It was also easy to ramp up production over the course of one year to over 10,000 units a month. In short, it was a smaller, more transportable, and less expensive rifle than the AR-­10.

Brownells-BRN-180-2
Brownells-BRN-180-3
Photos by Mark Fingar. The charging handle, bolt carrier group and recoil springs are true to the original design. The BRN-180 operates identically to the AR-180.

There was some interest in the AR-­16, but it never secured any significant military contracts. In keeping with the tradition established by the AR-­10/AR-­15, it wasn’t long before ArmaLite miniaturized the AR-­16 into the AR-­18.

Jim Sullivan once told me “Eugene Stoner was a .30-­caliber man and wanted nothing to do with a .22.” That was the reason designing the AR-­15 was left to Sullivan and designing the AR-­18 was left to Arthur Miller, the head of design at ArmaLite after Stoner’s departure.

Miller’s AR-­18 brought back some of the AR-­10/AR-­15 features that Stoner left off his AR-­16. The AR-­16 has no magazine well. Instead it uses a “rock and lock” technique to attach the magazine to the lower receiver. Miller brought back the magazine well with the push-­button magazine release.


Like the AR-­16, AR-­15 and AR-­10, the AR-­18 retained Melvin Johnson’s rotating bolt and locking barrel extension. The difference is the AR-­16 and AR-­18 seat the bolt in a square bolt carrier that rides on two guide rods, each with its own recoil spring.

When fired, the bullet moves down the bore past the gas port. Gas moves through the port and fires a short-­stroke piston. The piston impinges on the shorter carrier and that cycles the action. By using stamped metal for the receivers, the cost for the AR-­18 was considerably less than the M16.

Brownells-BRN-180-4
Photo by Mark Fingar. A polymer dust cover helps to keep debris out of the receiver until the rifle fires.

BRN-180 Upper Receiver Group Specs

  • Type: Short-stroke, piston-operated, semiautomatic
  • Cartridge: .223 Rem/5.56mm NATO
  • Barrel Length: 16 in.; 1:8-in. twist
  • Overall Length: 24.75 in.
  • Weight: 4 lbs., 9 oz.
  • Finish: Type III, hardcoat anodized
  • Sights: None
  • MSRP: $800
  • Manufacturer: Brownells, brownells.com

AR-­18 To BRN 180

The AR-­18 received a lot of attention from the U.S. military between 1964 and 1969, where it fared well in military trials. However, it didn’t do well enough to unseat the recently ascendant M16.


Knowing that the U.S. military wasn’t going to bite on the AR-­18, ArmaLite began producing a semiautomatic version of the rifle for commercial sales. The semiauto variant was called the AR-­180. It did very well because it had very similar features to the M16, was less expensive and looked a little more conventional than the M16.

Some of the original AR-­180s were made in California, but Howa in Japan and Sterling Armament in the United Kingdom made the vast majority. These rifles sold well and stayed in production until 1983.

Brownells has been spending a lot of time and effort bringing back the classic rifles that shaped weapon innovation back in the 1950s and ’60s. They have the origins of the AR-­10 and AR-­15 covered in great detail, so it seemed only natural to breathe some new life back into the AR-­180. Brownells calls their version the “BRN-­180” and it takes the best features of the AR-­180 and combines them with features that most shooters demand today.

The BRN-­180 retains the dual guide rods, recoil springs and piston assembly of the original AR-­180, as well as the short seven-­lug rotating bolt and squared-­off bolt carrier. The BRN-­180 also retains the dust cover that keeps dirt and foreign debris from entering the ejection port.

Where the BRN-­180 diverges from the AR-­180 is the absence of a sheet metal upper receiver and plastic handguard. In the place of those two items is a machined-­from-­billet 7075 T6 upper receiver and a 14-­inch M-­LOK free-­floating handguard. Both are significant improvements over the original.

Brownells-BRN-180-5
Photo by Mark Fingar. The fixed charging handle reciprocates when the rifle fires. The rifle does not come with sights. The ones seen here were added for accuracy testing.

Relevance Today

Far from being just a cool way to reconnect with the past, the BRN-­180 offers today’s shooters some easily identifiable advantages over modern piston designs.

For instance, AR-­15s that have piston operating systems can suffer from carrier tilt. It’s a condition where the back of the carrier tilts down from the piston’s pressure on the carrier key causing the carrier to rub aggressively on the front of the buffer tube when cycling. Over time this can cause a knife-­edge to form on the front of the buffer tube. The BRN-­180 will never have this problem because the carrier never leaves the upper receiver.

Another advantage to the BRN-­180’s design is since the carrier never leaves the upper receiver, any AR-­15 pattern lower receiver hosting the BRN-­180 can have a folding stock. LAW Tactical makes an adaptor that fits any AR-­15 lower receiver and the SIG Sauer MCX stock can be made to fit any AR-­15 lower receiver as well.

Putting a side-­folding stock on a rifle is the single best way to make it easily transportable and storable. The rifle case you need is smaller, so getting it up and down stairwells is more convenient and finding a place to store it when not in use is also easier.

The convenience of being able to fold the stock on an appropriately equipped lower receiver with the BRN-­180 cannot be overstated. However, unlike the AR-­15, the BRN-­180 can be fired repeatedly with the stock folded. That certainly isn’t the preferred way to fire the rifle, but it is possible should circumstances require it.

The BRN-­180 has a couple of unique features that make it an ideal suppressor host. The first is the piston operation system. Most of the gas in any semiauto that exits the ejection port comes back down the barrel and not through the gas tube. Every comparison I’ve done with a direct-­impingement AR and a piston-­operated AR has shown that there is almost always a little less gas in the shooter’s face when shooting a piston system.

Beside its piston operation, the BRN-­180’s upper receiver also lacks the opening in the receiver’s rear for a charging handle. This restricts even more gas from reaching the shooter. Since the BRN-­180 has no opening there, this further reduces the shooter’s gas exposure.

Brownells-BRN-180-6
Photo by Mark Fingar. The BRN-180 upper ships with two interchangeable piston cups. One is for suppressed fire and the other is for unsuppressed fire.

Since there is no way to swap buffer weights to help control bolt velocity in the BRN-­180, Brownells includes a spare piston cup that is optimized for when a suppressor is used on the rifle. Installing a suppressor on any semiauto barrel increases the amount of time the gas system remains pressurized. This increases bolt velocity and can cause malfunctions if not addressed. The role a piston cup plays is it starts venting gas sooner and in greater quantity than the piston cup that comes installed on the upper. The suppressor-­ready piston cup takes a couple minutes to install.

Other unique features about the BRN-­180 that it shares with the original AR-­180 are the ease with which it can be disassembled and the reciprocating charging handle. Disassembly (to include handguard and gas system removal) takes about 30 seconds and requires only a nonmarring hammer when the upper is new. Doing a detailed cleaning of every nook and cranny on the BRN-­180 is as easy as it gets. Even the bolt comes with a nickel-­Teflon coating for smoother operation and cleaning.

The reciprocating charging handle gives the shooter the option to manually control the bolt at any time. Easing the charging handle back to check for a loaded chamber and pushing it closed to ensure the bolt is seated are equally simple and speedy operations. Likewise, mortaring the rifle to remove a stuck case is an option should it become necessary.

The range performance of the BRN-­180 was what you’d expect from a new, high-­quality AR-­15. The barrel has a 1:8-­inch twist rate and the chamber is done in .223 Wylde, not an uncommon combination with some of the better AR-­15s out there.

For those folks who want a shorter version, Brownells also offers the BRN-­180S that features a 10.5-­inch barrel and a fully adjustable gas block for shooting suppressed or not.

The BRN-­180 represents a really cool and modern look at another iconic Stoner-­inspired rifle. In addition to the history that accompanies the BRN-­180, it is ideally suited to suppressor use and is easier to store and transport than a comparable AR-­15. While it is unlikely the BRN-­180 will ever unseat the AR-­15 in popularity, it definitely has a place in the safe and on the range.

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