Review: CMMG 9mm MKGS Guard DRB2

Review: CMMG 9mm MKGS Guard DRB2

As Shooting Times has reported many times, the folks at CMMG are an innovative bunch. A good example is the MkGs series of AR-15 carbines.


The MkGs series includes the 9mm BANSHEE and the 9mm GUARD. The BANSHEE model is an NFA gun that features a 5-inch barrel. The 9mm GUARD, which is the gun I am reporting on here, is offered in MkGs DRB, MkGs DRB2, MkGs PDW (also an NFA gun with an 8-inch barrel), and MkGs T configurations, and all of them utilize a lower receiver that’s specifically designed to use Glock 9mm pistol magazines. Our sample is the MkGs DRB2 configuration, and it came with two 33-round magazines that bear the Glock logo.

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The MkGs GUARD uses CMMG’s proprietary Radial Delayed Blowback system wherein the bolt is forced to rotate and unlock, slowing the bolt carrier group enough to safely cycle.

The Nuts and Bolts

The 9mm MkGs GUARD features CMMG’s Radial Delayed Blowback operating system. The system uses a bolt that is forced to rotate and unlock, slowing the bolt carrier group enough to safely cycle. According to the company, the benefits of Radial Delayed Blowback are a reduction in the weight of the carrier and buffer, resulting in a lighter-weight carbine and, surprisingly, less felt recoil than with a straight blowback system. The MkGs GUARD also features a new patent-pending, dual-pinned, fully machined bolt-catch linkage.


The MkGs GUARD’s lower receiver is made from 7075-T6 aircraft-grade aluminum, and the upper is also 7075-T6 aluminum. The DRB2 version comes with a Magpul CTR six-position collapsible buttstock and a Magpul MOE pistol grip.

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The CMMG 9mm MkGs GUARD accepts Glock pistol magazines. The DRB2 carbine used for this report came with two 33-round Glock magazines.

The 9mm MkGs GUARD DRB2 has a 4140 chrome-moly, medium-taper, 16-inch, 1:10-twist barrel; a CMMG SV muzzle brake (the barrel is threaded 1/2-28 to accept most common 9mm suppressors); and CMMG’s 14-inch-long free-floating KeyMod handguard. Like other 9mm ARs, the GUARD has a shell deflector, but unlike some pistol-caliber ARs, the GUARD has a forward assist.

The DRB2’s upper, lower, and handguard are finished in Cerakote (sniper gray for our sample). The trigger, charging handle, forward assist, safety lever, magazine release, pivot pin, takedown pin, bolt carrier, ejection port cover, barrel, muzzle brake, buttstock, and pistol grip are black. The gun weighs 6.2 pounds unloaded, and it comes with a full-length flat-top Picatinny rail. There are no sights.


The DRB2 features a Geissele SSA single-stage trigger, and the trigger pull of my sample carbine was good, measuring a consistent 4 pounds, 10 ounces. Other versions of the 9mm GUARD use CMMG’s own single-stage trigger, and the muzzle brakes, buttstocks, and handguards also vary. Other colors of Cerakote are available, as is an all-black option. You also can upgrade to an M-LOK handguard for an additional charge.

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The DRB2 version also comes with CMMG’s SV muzzle brake. The barrel is threaded 1/2-28 to accept most common 9mm suppressors.

Shooting the 9mm GUARD

CMMG’s 9mm MkGs GUARD offers all the features one could want in a defensive carbine, but the real test is in how the gun handles and shoots. Because the focus of this article is on defense—particularly home defense—I installed a SIG SAUER ROMEO4H red-dot optic for the shooting session (see the accompanying sidebar for details about the optic), and I fired five, five-shot groups with each of the five selected factory loads from a benchrest at a distance of 50 yards and averaged them. As you can see in the accompanying chart, the GUARD’s best average accuracy came with Nosler’s Match Grade 124-grain JHP ammunition. That load averaged 1.55 inches at 50 yards. The other factory loads all averaged less than 2.25 inches, with the largest average accuracy coming in at 2.11 inches. Overall average accuracy at 50 yards for all five loads was 1.84 inches.

Then I loaded a couple of magazines all the way up, randomly varying the types of ammo, and fired the carbine offhand on a man-sized silhouette target set at 45 feet, which is the distance of the longest straight shot possible through my home. I ripped off the shots as quickly as I could while carefully maintaining as precise of a point of aim as I could manage, and the carbine put all 66 rounds in a nice cluster measuring 1.48 inches. Throughout my shooting, the 9mm carbine digested all ammo fed to it without a hiccup, even when I mixed the various rounds in the magazines.

Looking at the velocities, through the 16-inch barrel, the ammunition produced velocities from 979 to 1,469 fps. Those figures are between 69 and 278 fps higher than the velocities for the same ammunition produced in the 4.02-inch-barreled CZ-USA P-10 C pistol featured in the gun review by Joel Hutchcroft elsewhere in this issue of Shooting Times. That’s entirely understandable due to the carbine’s four-times-longer barrel. The velocity increase between the carbine’s barrel and the pistol’s barrel calculates to be between 5.76 and 23.2 fps per inch.

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The DRB2 version has a Geissele SSA single-stage trigger. Our sample’s trigger pull averaged 4.63 pounds.

If you’re wondering why anyone would want a 9mm AR for defense, Joseph von Benedikt has written for Shooting Times, “where home defense is concerned, AR-type carbines chambered in 9mm have several advantages over ARs chambered in .223/5.56 or any of the other popular rifle cartridges. Fired from a 16-inch AR-15 carbine barrel, a 9mm cartridge is relatively quiet, as cartridges go. Another huge benefit a 9mm AR offers is the simplicity of its operating system. Unlike rifle-cartridge ARs, which operate off of a complex gas-impingement system that bleeds gas from the bore and feeds it back into the action to unlock and drive the bolt and carrier, 9mm ARs function via a simpler blowback system. No gas tubes, no pistons, no gas rings.”

As I stated earlier, the 9mm MkGs GUARD DRB2 proved to be 100 percent reliable. In addition, it was comfortable to shoot. I have to admit I was surprised just how soft-shooting it was. And it was accurate, too. Plus, with the SIG ROMEO4H mounted, it was fast to get on target. Making double- and triple-taps on the silhouette target was a breeze. It performed exactly how you want your home-defense carbine to perform.

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