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[Build Sheet] Short & Sweet: Brownells Piston-Driven Blackout

Brownells is a huge player in the AR-15 aftermarket, so it came as a bit of a surprise when they jumped full bore into the black rifle scene with Stoner’s other carbine. 

It’s arguable that the AR-18 is a more successful design than the AR-15, as its fingerprints can be found in the majority of military small arms of the late 20th and early 21st centuries. The entire list reads like a who’s who of desirable guns — the G36, BREN, SCAR, FN2000, AUG, T91, VHS, Daewoo K1, Howa Type 89, and GROT. 

Oh, and the SA80. All use a short-stroke gas piston to drive a carrier that holds a rotating, multi-lug bolt. 

The BRN-180 recreates Stoner’s recipe but is adapted to modern manufacturing methods, mating to an AR-15 lower receiver and offering the best of both worlds — you get the suppressor-friendly benefits of a short-stroke piston with the broad aftermarket support of America’s favorite rifle. 

With the introduction of the latest BRN-180 variant, we decided to take advantage of the situation to create a compact 300BLK carbine as a multipurpose truck gun and hog slayer. 

The latest version of the BRN-180, the BRN-180SH, features a three-position gas block, allowing the user to shut off gas flow completely to eliminate action noise during the shot and effectively transforming the gun into a straight-pull bolt action. 

Note that you’ll need a tool such as a bullet tip to change settings, but if you don’t have one of those handy, you won’t be shooting much anyway. It also has a turned-down charging handle made from machined aluminum that’s a bit lower profile than the original dogleg steel version. 

Its 10-inch, 1/8-twist barrel does a good job of stabilizing 220-grain projectiles at subsonic velocities, and we’d expect the nitride finish to hold up well in this application, resisting wear at least as well as chrome lining. 

Aiming the carbine is addressed by a Primary Arms SLx 1x MicroPrism sight, teamed with one of their 3x magnifiers in a flip-to-side mount. We’re constantly amazed at the value PA is able to cram into their optics, and the 1x prism is one of our favorites for a number of reasons. 

Built on a forged and machined aluminum housing, the glass is surprisingly clear for a budget optic, and the illumination settings cover all our needs, from night vision to Arizona midday summer sun. As it’s an etched reticle, it isn’t dependent on batteries, though it does mean you have to set it up like an LPVO — unlike a red dot, it doesn’t have unlimited eye relief. 

We found the rearmost Pic rail position to be perfect for the magnifier, but if you’re planning on using the micro prism as a stand-alone sight, you’ll be better served by moving it rearward to minimize scope shadow. If you’d prefer a QD mount, rather than the supplied one that uses Torx head screws, then fear not — the micro prism uses an ACOG interface, so your choice of ADM, GDI, or Midwest Industries will fit.

Our lower is from a SIG MCX, which has a Pic rail interface where the buffer tube would normally be on an AR-15. This allows a choice of stocks, including the Ruger folder we used here and scavenged from the 5.7 cover gun in RECOIL Issue 64. 

We could’ve simply used a BRN-180 lower or a Pic rail adapter mated to an AR-15, but we already had the SIG SBR’d and ready to go. The only other modification made to the lower was to install a Geissle SSA trigger, cleaning up the pull. 

No defensive carbine is complete without a sling and a weapon-mounted light, and we’re fans of both items featured here. Dan Brokos’ LFT sling is cutting edge in terms of its materials, and it’s comfortable, lightweight, and versatile, while SureFire’s Mini Scout Light Pro offers a decent amount of illumination and takes up a minimal amount of space — useful when you’re limited by a short handguard. 

Because this is a .300BLK build, it’d be just plain wrong not to add a can, and in this case, we went with one of the most versatile models on the market. The SilencerCo Omega 36M will handle up to 9mm diameter projectiles and is rated for calibers up to 338 LM, so the comparatively small amount of gas produced by the Blackout is handled easily in its short configuration. 


  • Brownells BRN-180SH upper: $999
  • SIG MCX SBR lower: n/a
  • Geissele SSA trigger: $245
  • Ruger 5.7 Carbine folding stock: n/a
  • LFT sling: $59
  • Primary Arms SLx 1x MicroPrism sight: $270
  • Primary Arms SLx 3x magnifier: $180
  • Surefire M140A Micro Scout Light Pro: $309
  • SilencerCo Omega 36M: $1,169

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