DIY AR-180 Build From a Brownells BRN-180 Upper

By Adam Green On May 8, 2024

When you think of the AR platform, you think of that letter sequence followed up by a 10 or a 15, as you should, because the ArmaLite company designed them and sold the design that eventually spawned into two of the most iconic rifles ever amongst military, law enforcement and commercial markets. ArmaLite was not a manufacturer though. They were actually a design firm. Their mission was to design the most advanced rifles in the world and license them to the top gun manufacturers who could mass produce and sell a finished product for them.

Originally ArmaLite wanted to sell the AR-10 and AR-15 themselves but decided they didn’t really want to deal with the politics of selling firearms, which ultimately lead to the sale of the AR-10 and AR-15 patents and production rights to Colt in 1959. The heart of both of those weapon systems was Eugene Stoner’s direct impingement gas system. However, when the patents were sold, Stoner could no longer design guns using direct impingement. This forced him to go back to an old design he came up with. The short-stroke piston system. He started designing what he was calling an AR-16. This was a select-fire rifle chambered in 7.62x51mm. Unfortunately, that design never left the prototype stage, scrapped just before Stoner departed the ArmaLite company.

The AR-16 later became the base for the AR-18, but ArmaLite tried to keep cost down and used stamped steel receivers instead of forged aluminum like their previous successes, the AR-10 and AR-15. This new system utilized three main components: the operating rod, the cylinder, and the operating rod link. The piston attached to the front sight base. On the operating rod is an operating rod spring that returns the operating rod to its forward position once the bolt has been struck and pushed to the rear.

Due to the use of the piston/operating rod, there were no hot gases brought into the bolt carrier group, resulting in a much cleaner rifle that required far less maintenance than the AR-15. The AR-18 failed to garner much attention. It later made its way to the civilian world, introduced as the AR-180, a semi-auto version of the select-fire AR-18.

The Brownells BRN-180 Upper

Fast forward to 2019 and Brownells decides to team up with PWS to create a new variation of Stoner’s AR-18 design with their own modern twist. Meet the BRN-180 upper receivers, and later came the BRN-180M lower receiver to complete your builds properly. I fell in love with this design when I spotted the AR Pistol setup at SHOT Show and knew I needed to build one. So I ordered a BRN-180SH complete upper receiver with a 10-inch barrel chambered in 300 Blackout. I also ordered the BRN-180M Lower even though you can use any Mil-Spec lower with the uppers.

I loved the integral 2-inch-long, four-slot Picatinny rail in place of the buffer-tube port on the lower, which is why I went with it. This allowed me to install the SB Tactical FS1913 folding Pistol Brace very easily on my build, since I was building a pistol with the goal of creating the ultimate truck gun. The lower takes standard AR-15 parts, including a standard AR-15 trigger, making it very easy to build out exactly as you want since the parts are readily available. I opted for a Rise Armament Blitz trigger and utilized an Anderson Manufacturing lower parts kit and pistol grip.

Brownells components provided the backbone for the AR-180 build.

Cooking With Gas

The upper I ordered uses the new BRN-180SH Suppressor Optimized system. The upper receiver includes a gas shutoff setting and an adjustable charging handle attached to the side of the bolt. The charging handle can be pointed downwards like a bolt action rifle. So the BRN-180SH can be configured into an extremely quiet, fast-charging single-shot firearm. Simply adjust the gas system off, then pull the charging handle back and release to cycle the bolt. The single-shot function eliminates gases escaping from the ejection port, making for even quieter operation.

If I choose to shoot semi-auto, the gas system can simply be set to the suppressed or unsuppressed setting by simply using the provided tool to reach into the cutout in the handguard and turning the gas adjuster. You can also move the charging handle to the upward position to get it out of the way when shooting semi-auto. The upper features an M-LOK handguard with a full Picatinny rail on top, which made it easy to mount my Meprolite M22 red dot optic as well as some M-LOK accessories from UTG Pro. I went with the M22 because the goal of this build was to create an extremely reliable truck gun, and the M22 from Meprolite doesn’t utilize any batteries that can die. It uses Tritium and fiber-optics to ensure that no matter what the conditions are you will always have a dot to rely on.

A Brownells AR-180M lower helped complete the build.

Rounds Downrange

On the range I quickly realized why I built this gun. It is an absolute beast but also tame enough that anyone can shoot it with ease. I figured being tiny with a folding brace this pistol would be violent and hard to control, but it is actually the exact opposite. It handles recoil extremely well, and the piston system just runs no matter what.

I had a friend who had never shot an AR before shoot the gun, and she had no issues at all and fell in love with it immediately as well. It chewed up spit out everything I threw at it, including Remington UMC 220-grain, Fiocchi 150-grain, and Hornady 190-grain subsonic rounds when I tried it suppressed. I ran it using the single-shot gas setting both suppressed and unsuppressed and ran it on the other settings as well. I never had a single issue or malfunction except when I ran it on setting one with a suppressor on the front. That is my fault though and not the gun’s fault at all.

If you are looking to build an easy AR but be a bit different than all your friends, I definitely recommend checking out the BRN-180 and BRN-180S line of upper receivers. Brownell’s makes the uppers in both pistol and rifle lengths chambered in.223 Wylde, .300 Blackout, and 7.62x39mm. The fact you can fire these without a brace or with the brace or stock folded puts them in a totally different category as far as I’m concerned and is the reason I now carry this pistol in my truck daily.

Check out the full lineup at brownells.com.