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Meet the FourSix: The First 4.6x30mm Caliber AR-Style Rifle

FourSix rifle. Image Credit: Sandboxx.

Meet the FourSix: The 4.6x30mm caliber has long been one of only two rounds used in personal defense weapons (PDW). Of the two rounds, the 4.6x30mm has only been used in a single weapon, HK’s MP7. Well, until this point. But now, thanks to CMMG, the 4.6x30mm has also graced the AR platform with the release of the FourSix.

The MP7, specifically the MP7A1, has been utilized by the Elite Frogmen of SEAL Team 6, aka DEVGRU, for numerous applications. In fact, MP7s were present when the SEALs took down bin Laden. It’s an interesting and compact package and the 4.6x30mm grants it superior range and penetration compared to a standard pistol cartridge. It’s also well proven by American police and military forces, as well as elite counter-terrorism forces around the world.

The FourSix brings the 4.6 round to an AR platform and opens the round up to entirely new markets. The benefit of the 4.6x30mm is that it is extremely easy to control and has very little recoil. Users get a flat shooting cartridge with the potential to reach out to 150 yards and offer substantially more penetration.

The round itself uses a spitzer bullet that’s more in line with a rifle round than a pistol cartridge. Yet it’s quite short and ultimately falls between a pistol cartridge and a rifle cartridge.

The FourSix – It’s all AR

The AR 15 platform is by far the most popular rifle platform among military and police forces, as well as the civilian population. The platform has long been modular, easy to use, reliable, accurate, and capable. The FourSix is all AR 15.

This includes the use of a direct impingement (DI) system versus the blowback system often utilized by submachine guns. Benefits of the DI system include lower recoil, lower weight, and a high degree of reliability.

The controls match the AR-15 platform, so transitioning from an M4 or M16 to a FourSix won’t require much retraining. The benefit of the FourSix is that it’s even shorter and lighter than the smallest of 5.56 caliber rifles. You can only trim the barrel of a 5.56 rifle so much while keeping it effective. The FourSix delivers an eight-inch barrel that’s extremely effective with the 4.6x30mm round.

Additionally, a military or police force could purchase FourSix upper receivers and drop them onto lowers that are already in service. This could allow rifles to become PDWs within minutes.

For police and military use

The current incarnation of the FourSix is aimed at the everyday civilian market and comes as a standard AR without any features to make it run afoul of the National Firearms Act. However, CMMG has in the past sought military and police contracts. Specifically, they entered the Mk4 into the Army’s SCW program.

In that contest, they submitted an SMG variant of the weapon that utilized a proper stock and select-fire capability. The FourSix is a part of the Mk4 Banshee series, and the only real difference is the caliber and magazine configuration.

Taking the FourSix to a short-barreled rifle or SMG variant wouldn’t be difficult. The HK MP7 is an exotic and expensive weapon. The CMMG variant gives you the same range, penetration capabilities, low recoil, and accuracy of the MP7 without its price tag.

Currently, the short rifle dominates the market in the military and police world. As we see from the MP7, the Army’s SCW program, and other small projects in the United States military, the desire for an SMG-sized weapon exists. The FourSix gives you the controllability of an SMG with the handling and accuracy of an assault rifle out to 150 yards.

The FourSix vs. the MP7

The MP7 beats the FourSix in numerous ways. First, it’s much smaller. It has a total overall length of 25.1 inches, with the stock extended. If you fit the FourSix with a stock and fully extend it, the total overall length is about 26.9 inches. With the MP7’s stock collapsed, the gun is only 16.3 inches long.

It’s very handy, and with the magazine in the pistol grip, the balance allows it to be controlled with ease when using a single hand in semi-auto. This makes the MP7 perfect for dog handlers, motorcycle cops, and similar roles.

However, the AR platform offers numerous advantages. First, it’s an AR, and the training gap between the MP7 and the M4 is broad. The gap between the M4 and the FourSix is tiny. CMMG’s magazines are the same dimensions as an AR mag, and this allows the use of MIL-SPEC lowers.

Shooters could drop a FourSix upper onto an M4 lower and simply swap the buffer, making their M4 is a much shorter and lighter PDW. CMMG’s magazines will fit into standard M4 magazine pouches as well.

The MP7’s wire stock and short nature make it all about red dots. It’s not great for really reaching out to the 150 yards the 4.6x30mm round is capable of. The FourSix, with a proper stock, makes it easy to mount a 1-4X optic to take total advantage of the range of the round.

A tool

The use of multiple uppers has gained a degree of popularity with the United States military, especially within the Special Ops community. Dropping a FourSix upper onto an M4 lower gives the user another tool for specific tasks. The benefit of the 4.6x30mm versus the 5.56 is the ability to make the rifle much shorter without compromising reliability or controllability.

300 Blackout works very well in short barrels, and for most tasks when you need to go super short, the 300 Blackout works better. However, in a very small niche, the 4.6x30mm might be a better option. For ultra-tight close quarters, like the bridge of a Chinese ship, the controllability of the 4.6x30mm on full auto could be massively beneficial.

I don’t see the FourSix or the 4.6x30mm replacing assault rifles by any means, but I could see why it would replace 9mm submachine guns. The 4.6x30mm pierces armor, flies further, and is extremely easy to control. It’s a niche caliber, and the FourSix and MP7 are niche weapons, but the caliber has proven its effectiveness.

Travis Pike is a former Marine Machine gunner who served with 2nd Bn 2nd Marines for 5 years. He deployed in 2009 to Afghanistan and again in 2011 with the 22nd MEU(SOC) during a record-setting 11 months at sea. He’s trained with the Romanian Army, the Spanish Marines, the Emirate Marines, and the Afghan National Army. He serves as an NRA certified pistol instructor and teaches concealed carry classes. This first appeared in Sandboxx. 

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Sandboxx News is a digital and print military media outlet focused on the lives, experiences, and challenges facing today’s service members and America’s defense apparatus. Built on the simple premise that service members and their supporters need a reliable news outlet free of partisan politics and sensationalism, Sandboxx News delivers stories from around the world and insights into the U.S. Military’s past, present, and future– delivered through the lens of real veterans, service members, military spouses, and professional journalists.