CMMG has never been afraid of doing unusual things with the AR platform. They created the Mutant, an AR that uses AK magazines. They designed the radial delayed blowback system that tames recoil in a simple way. Now, they have created the first civilian firearm to chamber the 4.6x30mm cartridge and the first AR that chambers the round. CMMG’s new FourSix joins CMMG’s Banshee lineup, but doesn’t use the radial delayed blowback system.
Instead, the FourSix is a direct impingement gun with CMMG’s own micro length gas system and their new micro gas block. It’s a tiny system that completely eliminates the downsides associated with blowback-operated firearms. CMMG sent me the FourSix with 400 rounds of 4.6x30mm from Fiocchi. This 40-grain ammunition reaches 1,900 feet per second and is absolutely adorable.
The FourSix and the 4.6x30mm cartridge
The 4.6 rounds are .18 caliber and extremely small. The round was developed for HK’s own MP7 PDW. These tiny rounds offer more range and penetration than a typical 9mm round.
The round was primarily designed to defeat soft armor and provide more range than a 9mm round. Like the 5.7x28mm, the 4.6 lacks muzzle energy, but the 4.6×30 can tumble and yaw like a 5.56 round.
The super-secret bubbas of SEAL Team Six carry the MP7, and they carried them during the bin Laden raid. The round penetrates deeply and can reach the FBI required standards. At the same time, you get a decently flat shooting cartridge between 100 to 150 yards.
Breaking The FourSix Down
The CMMG FourSix is an AR pistol with an eight-inch barrel finished off with the CMMG SV Brake. The 4.6x30mm round is made for the MP7’s 7.1-inch barrel, so it’s actually moving beyond MP7 velocities. Velocity is the key to the 4.6’s success, so I’ll take more if I can get it.
The FourSix comes with an M-LOK handguard, flat top upper, and everything else you come to expect from a modern AR design. The handguard doesn’t have much room, but you could squeeze on an M-LOK foregrip if it’s an SBR, or an AFG for apistol. The CMMG RipBrace makes an appearance, too. This brace allows you to set the ‘stop’ point, and the brace can be yanked automatically to that point. Just grip and rip.
The charging handle is an ambi extended CMMG design, and Magpul MOE rounds things out at the pistol grip.
Now I know what you’re asking: What’s the magazine pattern? Well, it’s proprietary because it has to be at this point. However, it’s not a bad proprietary.
CMMG made a polymer magazine that’s essentially the exact same dimensions as any other AR-15 magazine. Therefore you can purchase the upper and use your own MIL-SPEC lower, and the magazines will fit.
FourSix magazines also fit in standard AR-15 magazine pouches, so that’s a plus. They hold 40 rounds of the 4.6x30mm and function with a standard LRBHO (price is $39.95 each).
I think the mags were a brilliant move. MP7 magazines are tough to find and cost anywhere from $80 to $120 dollars a piece. Plus, the CMMG mag design allows builders to use their own lowers, and magazines pouches are aplenty.
The FourSix Ergonomics
As an AR-15 design, the ergonomics are exactly what you’d expect. To me, they are either excellent, or I’ve somehow been brainwashed by the Stoner design as a result of its cultural domination.
One nice feature is the ambidextrous safety and massive charging handle. That charging handle is enormous, and you can do the super fancy and super tactical ‘blade’ engagement to charge the gun if you want.
If you’ve never handled an AR-15, you’ll quickly find the controls are easy to engage, especially if you are a right-handed shooter. The magazine release can be easily engaged with your trigger finger. The safety can be quickly manipulated with your thumb, and it clicks and pops nicely to let you know when it’s engaged. The bolt release requires a quick slap, and the bolt slams home.
It’s all very straightforward and there’s a reason why you can take an 18-year-old who’s never shot a firearm and have them making regular 500-yard shots after a week of practice in boot camp.
What stands out about the FourSix to me is its weight. It’s a very lightweight, svelte five pounds, six ounces. The gun’s overall length with the brace fully deployed is 26.9 inches. It’s light, it’s short, and very easy to control.
At the Range
The little 4.6x30mm round promises to fly fast and hit hard, but how does it perform? Well, it handles like a very loud rimfire round. Seriously, it’s a joy to shoot, and recoil and muzzle rise are insignificant. My double taps are almost right on top of each other because the gun doesn’t buck or jump. It’s super easy to handle, and the CMMG FourSix makes dumping half a mag an easily controllable affair.
My young son — under my supervision — handled the FourSix like it was a Ruger 10/22. We destroyed an ornery and vicious looking soda can at 10, 15, and 20 yards. Back to 25 yards, he kept a Champion gopher target spinning.
That ultra-low recoil makes it a lot of fun to shoot and very easy to handle. Even using one arm, I could control the gun and be reasonably accurate inside of 50 yards on a man-sized target.
I used the Crimson Trace CTS-1000 red dot, but honestly, I feel like I needed a magnified optic to get the most out of this gun’s effective range.
At 100 yards, I had about 4 inches of drop, and at 150, I saw around 9 to 10 inches. Not bad at all for such a small round, and it outperforms the 9mm at these ranges.
One hundred fifty yards might be maxing it out, but this is clearly a 100-yard gun, and inside that range, it absolutely owns. Hitting a 6-inch gong at 100 yards is a ton of fun with an AR pistol.
Why the FourSix?
The CMMG FourSix would be a solid little defensive weapon. It’s light and short, and the recoil makes it absurdly easy to control and use. I can drop a half dozen rounds in no time at all without any real deviation due to recoil and muzzle rise.
At 20 yards, I shot four gongs fast as I could. The gongs range from 4 to 8 inches in size, and I went four-for-four in under 3.5 seconds from the low ready and did so consistently.
As a defensive caliber, the 4.6 penetrates deep enough to reach the vitals, and the extremely low recoil ensures you can put lots of the rounds there. It lacks the expansion of a 9mm bullet, but does yaw and tumble due to the sectional density of the spitzer-style round.
From a practical perspective, the light and handy design make it a great little gun for picking off small game and predators. It’s accurate and flat shooting enough for me to feel confident headshotting rabbits and even coyotes.
CMMG’s little FourSix has brought one more caliber to the AR’s table. It’s a very capable little round that performs almost identically to the 5.7x28mm, but could be cheaper if demand rose and we get those famed economies of scale. The FourSix is a sweet little shooter and could be the perfect option for someone looking for centerfire reliability, increased lethality, but with rimfire recoil.
Specifications: CMMG FourSix
Caliber – 4.6x30mm
Barrel Length – 8 inches
Overall Length – 24.2 inches to 26.9 inches
Weight – 5lbs 6oz
Operating System – Direct Impingement
Magazine Capacity – 40 rounds
MSRP – $1399.95
Ratings (Out of Five Stars)
Ergonomics * * * * *
The FourSix utilizes the famed AR controls with an ambi safety and charging handle. CMMG kept the little gun short and light, which makes it sweet and easy to handle.
Reliability * * * * *
In 400 rounds, I had zero issues with ammunition extraction, ejection, firing, and feeding. The closest thing I had to a failure was the bolt failing once to lock on the last round., which might’ve been due to my magazine well grip and big hands.
Accuracy * * * *
No one will mistake this for a sub-MOA PRS gun, but for an 8-inch barreled PDW, the accuracy is more than respectable. I can drop rounds at 100 yards into small targets with great accuracy. I’m considering a 1-4 or 3X prism to really get the most juice out of FourSix.
Overall * * * * *
As the first weapon we mere mortals can own in 4.6x30mm, it’s tough to compare it to other firearms. Yet, the 4.6 round made a good jump to the AR platform, and it’s got me hooked. I hope 4.6x30mm takes off so ammo will get cheaper (yes, it’s available). The FourSix delivers an ultra-low recoiling, accurate, and fun-to-shoot platform, with a rather ingenious magazine solution.