The Unorthodox Trio: CMMG Rifles in 9mm, 6.5mm Grendel and .458 SOCOM

CMMG has long been an innovator, and the current lineup of AR-pattern rifles keeps with this tradition. Each one of the three rifles listed has multiple performance features, setting them apart from the more mainstream competitors.

Most CMMG guns are available in rifle and pistol configurations—and in 100, 200 and 300 series trim. The examples I have are all 300 series, which is the most upgraded version.

Actions and Accuracy

The Resolute 9mm rifle uses the same radially delayed blowback action that permits the use of .45 ACP and 10mm with a lightweight bolt attached to a separate carrier.

The bolt head stays effectively friction-locked against the barrel extension recesses, slipping out of engagement only after the gas pressure drops. This method permits a very light, clean system with a truly free-floated barrel.

Not surprisingly, this approach yields excellent accuracy around 2MOA with good ammunition, like Federal Syntech Match.

It also cuts down on the ejection port pop typical of plain blowback rifles, all without having to employ a heavy breechblock with correspondingly stout recoil spring.

The mechanical accuracy translates reliably into practical accuracy, thanks to the Geissele Automatics SSA 2-Stage trigger. Delayed blowback action and a highly effective muzzle brake keep felt recoil low even with the unpadded stock.

Stocks and Buttplates

The RipStock common to all three rifles deserves a special note. It’s an all-aluminum design with an integrated buffer tube and a slightly heavier-than-usual buffer. Its name stems from the design: any pull backward extends it to full preset length.

No level or release is involved in the extension, only in the collapse back to the storage configuration. Length preset is accomplished with a set screw underneath the buffer tube. Collapsed, this stock is very compact.

Extended, it’s quite robust, though the buffer tube itself is the limiting factor with the AR design. The downside is that it is practically a two-position (open/closed) stock, without the option to have a shorter length of pull for action and longer for deliberate target stance.

In 9mm, the textured metal buttplate isn’t a problem, but it needs a rubber recoil pad in heavier calibers like .458 SOCOM. A slip-on Hi-Viz rubber recoil absorber works as a stop-gap. CMMG may have a purpose-designed buttpad out in the future.

The buttplate already has screw holes for it. Aluminum also transmits warmth or cold readily to the shooter’s face, so a stick-on Neoprene pad is recommended.

Other Design Features

Safety selector lever and charging handle are both ambidextrous. Free-floated forend extends almost to the muzzle, permitting forward hand-hold for rapid fire or stable bipod position for prone.

The rifles come with two magazines each, but no iron sights, a reasonable omission in the age of almost universal optic use. The 9mm comes with two 30-rounders. I unboxed the MagPump mechanical loader for the occasion and was glad of that decision.

CMMG’s low recoil and high accuracy make shooting it as addictive as plinking with .22s, only with much more “oomph” behind each shot. I had no failures with any ammunition tried, from 115-grain ball to 147-grain subsonics and everything in-between.

The .458 SOCOM ships with metal “30-rounders” modified specifically to hold and feed 10 shots of .458 in a single stack.

Comparisons to Other ARs

Both 6.5 Grendel and .458 SOCOM were designed to fit standard AR-15 receivers, but the margin of safety around the boltface was a bit thin.

CMMG beefed up the receivers to be somewhere between AR-15 and AR-10 dimensions, resulting in a stronger, safer and milder recoiling platform.

Triggers interchange with AR-15; bolt and carrier do not. While CMMG AR-15s weigh in around 6.2-6.5 lbs., the guns mounted on hybrid receivers are 8.2-8.5 lbs—heavier, but a far cry from the beefier AR-10.

In the case of the 6.5 Grendel rifle, much of the extra weight comes from the target-grade barrel.

Test Conclusions

Between the mildly recoiling cartridge with a relatively high BC bullet, the stiff heavy barrel and a good trigger, this weapon hovers around 1MOA with match ammunition while remaining field-portable.

The .458 version isn’t quite as accurate, but it makes up in the sheer brute force of what is essentially rimless .45-70. At 60 yards, the average distance of U.S. police sniper engagement, it hits on a steel overlap.

Its recoil is noticeable, but not painful, being spread out over the long gas autoloading cycle. The lightest recoil was, as expected, with 140-grain ARX bullets.

These frangibles were also easiest on the steel targets, while 405 jacketed flat-point cratered steel and pushed the shooter more noticeably. The same bullet also cracked the 2×4″ wood supporting the steel with a single impact.

The rifle was fed a wide variety of .458 cartridges, including heavies with 500-grain flat-point bullets. These would work every bit as well as 12-gauge for bear defense, with the benefit of faster follow-up shots.

Besides these three calibers, Resolute rifles are available in eight others from .22 LR to .308 Winchester, pretty much for every taste and budget.

Which CMMG rifle would you choose? Let us know in the comments below.