CMMG Mk3 CBR Review

CMMG Mk3 CBR Review

CMMG_Mk3_CBR_Review_FCMMG has been in business for over a decade. It's one of those gun companies that, while not large or well known to the public, have always been well respected within the industry. For instance, CMMG's AR-15 magazine upgrade kit, consisting of a stainless steel non-tilting follower and braided wire spring, was the best in the business until Magpul came out with its design.

My first exposure to someone who owned a CMMG was in 2005 when I ran into a contractor just home from Iraq. As a driver, his primary weapon was an AR wearing a 7.5-inch CMMG top end, and it had served him well for months and gotten him through several firefights. Getting ARs that short to work reliably is no mean feat. So it was with interest that I heard CMMG is now producing a new line of .308 rifles: the Mk3.

CMMG offers five different variants of its Mk3 line, and for testing I secured a new CBR, which is the premier model in the line. It features a 16-inch black nitride-coated 416 stainless steel barrel with a 1:10 twist and tipped with CMMG's effective SV muzzle brake. The barrel has a tapered, medium-weight profile, which provides the right combination of stiffness and weight — meaning it is not so heavy you can't carry the rifle, yet not so light that the zero will start to shift after firing a few shots.

Overall weight is 8.7 pounds, which is a medium weight for a .308 AR. The empty rifle balanced over the front of the mag well. One 20-round Magpul PMag is provided with the rifle.


The barrel's gas system is as long as is possible with a 16-inch barrel. The port is only about 1.5 inches back from the end of the handguard. A longer gas system makes for a softer-shooting rifle and reduces wear on the moving parts because their velocity is reduced. (This is why the medium-length gas system is preferred for the .223/5.56 AR.)


The barrel is free-floated inside CMMG's RKM15 handguard. This is a one-piece, 15-inch aluminum handguard with the latest craze in attachment among the tactical types: KeyMod. There are KeyMod attachment points at three, six and nine o'clock all along the handguard, with a full-length Picatinny rail along the top.


Receiver fit was so tight that I couldn't see any daylight between upper and lower receivers forward of the trigger group area. The CBR is CMMG's premier model, and it sports a Geissele SSA trigger. Geissele makes some of the most well-respected triggers in the business, and the SSA provides a two-stage, 4.5-pound pull without adding any extra parts over the mil-spec design or using reduced power springs. Suggested retail on the SSA alone is $210.

The rifle has a Magpul MOE pistol grip and an ACS-L six-position collapsible buttstock. This lightened version of the ACS features one compartment for batteries/spare parts accessed from the right side and one slot sling attachment point, plus a quick-detach socket that you can mount if you want.

Negatives? I found only a few. The designers of the CBR deliberately went for a very clean, angular look, tending toward corners on the billet receivers rather than rounded edges. But the corners on the bottom of the trigger guard and the lower receiver above the trigger are not rounded off enough for my taste. They are nearly sharp. My test firing was done outdoors, with gloves, so I did not notice if the receiver corner was cutting into my finger.


Muzzle brakes seem to be all the rage due to the popularity of 3-Gun competition, but they are loud. CMMG already has a competition version of its Mk3, the 3GR, with the same effective (which means really loud) SV brake. I would have preferred a flash hider on the end of the barrel of this rifle — say, an AAC Blackout 51T. Once you add an optic and the weight of a loaded 20-round magazine to an 8.7-pound .308, recoil isn't bad even without a muzzle brake.

Also, for $2,000 I think CMMG could have included a set of flip-up iron sights, but I know the problem there. Whichever brand CMMG would have included, half of the customers would want something different. Overall my complaints are minor, and the rifle was reliable and nicely accurate with all loads tried — the two most important concerns.

The Mk3 CBR comes with a Magpul MOE grip and a 20-round magazine. It also features the excellent Geissele SSA trigger.
The fore-end has KeyMod slots, and the brake is CMMG's SV, although Tarr would've preferred a flash hider in place of the loud brake.
The lower is built from 6061-T6 billet aluminum and features a nicely beveled magazine well for fast, sure reloads.

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