The latest on-the-move firearm from Rock River Arms reaffirms that cross-compatible pistol ARs may be the smart choice for home and urban environment defense

by Rob Reaser

My wife has this recurring dream she sometimes gets when she’s under stress. The gist of it is that someone is in the house or breaking into the house. She has a gun but can’t find any cartridges to fit it. Everything she does find is the wrong size or type and won’t load. And in true dream fashion, sometimes the bullets are made of squishy foam; sometimes she has a rifle and can only find shotgun shells. Go figure.

Interestingly, her nightmare scenario has real-life parallels. In a true crisis, you don’t want to have to think about your reloads. When the mag is empty, you want to reach for the next one and go slap, rack, bang without any hiccups. In our house, we have six different firearm platforms strategically positioned—all of which employ different mags and cartridges. That is why a second loaded mag is placed next to each of the firearms. If we ever must use them, we certainly don’t want to add to the nightmare with another nightmare of not having an ammo resupply on hand.

For these reasons, an increasing number of defense-minded folks are taking advantage of cross-platform compatibility for their home and on-the-move defensive firearms. Specifically, they are matching ammunition and magazine compatibility to work across conventional pistols and rifles or AR-pistols.

The Rock River Arms RUK-9BT is a 9mm-chambered AR-platform pistol with GLOCK-style magazine compatibility.

With all the social upheaval and criminal activity that has exploded across the country this year, the case for cross-compatible, high-mobility firearms has never been greater. This is particularly true when discussing AR-platform pistols. Their short barrel configuration combined with a quality (and legal…at least for the time being) arm brace makes the AR pistol ideally suited for mobile carry in a vehicle or a backpack. Take an AR pistol chambered for popular defensive pistol calibers such as 9x19mm, .40 S&W, and .45 ACP and you have a firearm that can work alongside your EDC pistol.

One of the industry leaders in AR-platform firearms has placed a heavy focus on AR pistols since all the craziness began earlier this year. Over the last several months, Rock River Arms has come out with several AR pistols chambered for .223 NATO and 9mm. The ones that have caught our eye are the BT-9G series pistols that utilize a GLOCK-style magazine (the company also manufactures 9mm models that accept the Colt SMG mags). Our favorite of the lot is the ultra-short RUK-9BT with a 4.5-inch barrel. Sporting an SB Tactical arm brace, the RUK-9BT is no long-range master but for maximum portability on the road or on foot or for engaging a target in close-quarter environments, you’ll be hard-pressed to find better.

Before we go any farther, let’s kick the elephant out of the room. The SB Tactical arm brace is designed to help stabilize an AR pistol—meaning, an AR platform firearm sporting a sub-16-inch barrel. The inclusion of this arm brace instead of a conventional rifle stock is what excludes this firearm from being classified as an NFA weapon. In other words, it makes it a “pistol” instead of a short-barrel rifle. The design of the arm brace allows it to be braced against the forearm of the firing hand for legal operation. It can also be creatively employed to be supported elsewhere against the shooter’s body. Regardless of how you use the arm brace, the SB Tactical brace found on the RUK-9BT makes it a versatile firearm for defensive purposes.

As mentioned, the RUK-9BT is chambered for the 9×19 cartridge. Opinions may vary regarding the overall efficacy of the 9mm Luger when compared to, say, a .40 S&W or .45 ACP, but regardless of which way you lean, the 9mm is a proven defense round and is certainly the most popular defensive pistol cartridge on the market. In an AR pistol configuration such as the RUK-9BT, the 9mm Luger satisfies close-quarter performance while delivering cartridge compatibility with the most common pistol caliber. And if you happen to be running a GLOCK, that also means magazine compatibility. With a common magazine/cartridge caliber mix, you can buy your mags and load them in volume and always have what you need for either firearm platform. In a crisis, that eliminates the kind of stress, fumbling, and uncertainty that could keep you or someone you’re trying to protect from getting hurt.

To accommodate the GLOCK magazine, Rock River Arms utilizes their own billet aluminum lower receiver. The magwell is flared to make magazine insertions smooth and fumble-free. The mag release lever is located on the expected right side of the receiver. It features a large, serrated “button” end that is positioned ergonomically for easy magazine releases without losing your grip position. Simply reach up with your index finger, depress the button, and drop the mag.

Another feature we like about this lower receiver is the integrated winter trigger guard. It is machined into the receiver and is generously sized to accommodate gloved hands.

Moving to the upper receiver, we find an extruded aluminum A4 unit. RRA’s designers did an excellent job of blending the lines and contours of the upper and lower so that the assembled rifle has aesthetic continuity and a smooth visual flow—a refreshing departure from the many AR pistols out there that are put together to work but not necessarily to look good doing it.

As for the remaining operational and fire controls, the RUK-9BT sits in familiar territory, with the bolt stop and safety selector lever in the usual positions. The trigger is RRA’s two-stage model. The first stage take-up on our test model’s trigger wasn’t as smooth as what we’ve experienced with other RRA two-stage triggers, but there was a very positive stop at the end of the first stage (a plus in our book) followed by a crisp, decisive break. Overall, we feel it is an excellent pairing regardless of how you hold or mount the pistol for shooting. On the Lyman scale, the trigger averaged a 3-lb., 15.2-oz. pull weight.

Although the AR platform is a favored platform for post-purchase modifications and accessorizing, the RUK-9BT needs none of it. The grip is a top-tier Hogue with finger grooves that ensure a sticky hold and exceptional retention for one-hand shooting. For the handguard, RRA selected their own lightweight aluminum free-float model. At 4.25 inches long, it stretches out almost to the base of the Smith Vortex flash suppressor. Being M-Lok compatible, the handguard can accept a small light or laser, but our suggestion is to install a QD sling swivel mount instead since the SBA3 brace comes with a QD mounting hole.

RRA does install a Low-Pro hand stop on the handguard. Some may like it as it keeps your support hand from grabbing a hot barrel (and could help keep your hand away from the muzzle). It also provides a bit of push-pull support between it and the grip to help stabilize the firearm when firing in a non-braced position.

Atop the handguard is an integrated Picatinny rail, which mates to the upper receiver rail to provide the necessary acreage for open sights or an optic. RRA installs their NSP flip-up front and rear sights onto the pistol at the factory, so it is range-ready out of the box. The rear sight is a dual-aperture design. The larger aperture works well when holding the pistol with the firing hand extended, but you’ll need a cheek weld to get a clear sight picture when using the small aperture. For close-quarter engagement, just stick with the large aperture, if you are going to run with open sights.

Should you opt for a red dot, the RUK-9BT will accommodate. We installed TRUGLO’s Tru-Tec Micro Sub-Compact red dot for testing and it was ideally sized for this diminutive platform. Although it didn’t co-witness with the open sights, the red dot’s housing stayed below the sight picture when shooting open sights while the folded open sights stayed below the red dot’s sight picture. Good enough for us.

On the range, the RUK-9BT ran without a hiccup across four different factory loads and one custom load, with bullet weights spanning 115 to 125 grains. We even ran some subsonic 124-grain Black Hills ammo and experienced zero cycling issues. At 25 yards, our best group came from the custom loads, propelling Hornady’s XTP bullets for a five-shot group measuring .615 inches.

Is an AR pistol for everyone? Probably not. It can offer some unique fun on the range, for sure. For a 50- to 75-yard-plus target firearm…forget it. More novel than practical. As a close-quarter defense gun that you can tote in your vehicle or in a backpack or bugout bag, it makes a WHOLE lot of sense. Add in the ammo/mag compatibility with your home protection or EDC pistol and the question becomes, “Why wouldn’t you want one?”

Rock River Arms RUK-9BT Specifications

  • Caliber: 9x19mm
  • Lower Receiver: BT-9G billet aluminum
  • Upper Receiver: extruded aluminum A4
  • Barrel: chrome-lined 4.5-inch chrome moly, 1:10 twist
  • Muzzle Device: Smith Vortex flash suppressor, 1/2-36 thread
  • Trigger: RRA two-stage
  • Sights: RRA NSP flip-up front and rear
  • Handguard: RRA lightweight aluminum free-float, 4.25-inch pistol length, M-Lok-compatible
  • Arm Brace: SB Tactical SBA3 stabilizing arm brace, 5-position adjustable
  • Grip: Hogue rubber
  • Length: 23.5 inches extended
  • Includes: Low-Pro M-Lok-compatible hand stop, one GLOCK-compatible magazine
  • MSRP: $1,380
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