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CMMG Banshee .40 S&W PCC Review

The CMMG Banshee in .40 S&W gives what was originally promised – a screaming .40 carbine.

CMMG Banshee .40 S&W PCC Review

Photos by Mark Fingar

CMMG is a firearms company based in Missouri, and I suspect there may be something in the water there. Not just because they make really good ARs – they improve the AR design.

Their latest pistol-caliber carbine (PCC) is one from the Banshee line and is chambered in .40 S&W. Yes, that’s right, .40 S&W. Sure, the .40 has not gotten much love lately, but it has found a following at CMMG.

A Bolt Of Genius

The Banshee uses the company’s Radial Delayed Blowback (RDB) system, a clever modification to the AR bolt. On standard AR bolts, the rear of the lugs are square to the axis of the bore. They lock the bolt in place once rotated into the locked position. The force of firing won’t unlock them, so some outside force has to be used to rotate them to the unlocked position, allowing the system to cycle. That’s where the gas or piston comes in on standard AR platforms.

Since the bolt rotates, the cam pin is rounded, and the guide bar is notched.

On the CMMG RDB, however, the rear faces of the bolt lugs are machined at an angle. As a result, when a load is applied (the thrust of the cartridge when fired), the bolt wants to slip along that angled face, unlocking itself. But this takes time, as the weight of the bolt (and the pressure exerted on it) and the friction of the bolt in the carrier have to be overcome. There’s also a spring in the assembly helping to keep the bolt closed. This ensures that when the Banshee fully closes, it stays closed and doesn’t bounce or slip partially open on you.

The end result is a system that requires less mass to function properly. In a regular pistol-caliber carbine, the bolt is held in place by its mass. This is the same as any unlocked-bolt sub-machine gun (SMG), where the bolt mass and spring keep it closed long enough to not create a problem and cycle reliably.

On firing, the mass of the bolt has to be accelerated to the rear in a blowback system, and the more robust the cartridge, the greater the mass needed. (Or the distance traveled. But we can’t have two or three feet of receiver to soak up recoil.)

Since the RDB bolt rotates, there has to be a cam pin. That pin is round-headed on the Banshee, and the guide bar (what you might think is the gas tube) is notched for clearance on disassembly.

The lower is more compact, the magazine well is broached at the correct angle for a Glock magazine and it also has a magazine catch that works with unaltered Glock magazines.

A Mag-nificent Idea

The usual method of making an AR work with a pistol cartridge, after settling on a blowback system, is to modify the lower receiver to accept a SMG magazine. This used to be the Colt 9mm SMG magazine, itself a derivative of the Uzi magazine. Fitting it to an AR lower meant pinning in spacer blocks to fill the AR-15 magazine well.

The latest approach is to select a magazine that is lighter, common, inexpensive and easy to find. Enter the Glock magazine. This means the lower is more compact, the magazine well is broached at the correct angle for a Glock magazine and it also has a magazine catch that works with unaltered Glock magazines. The lower also has an integral triggerguard machined right out of the forging that has an angle in the middle to provide clearance.

Instead of modifying existing AR lowers, CMMG designed a lower made strictly for a PCC.

Freedom Of Choice

The Banshee can be had in one of three different build levels. The 100 Series pistols have their buffer tubes covered with foam and use an A2 flash hider. The 200 Series have a CMMG RipBrace installed and use a CMMG SV muzzlebrake. The 300 Series offers the RipBrace, your choice of muzzle device and an ambidextrous selector.

The barrel is 8 inches long, and in addition to being salt-bath nitride finished, it came with a CMMG SV brake installed.


The upper is a Mil-Spec M4 receiver, complete with forward assist and ejector lump. The rail on top meshes with the rail on the CMMG RML7 M-LOK handguard.


On the back, there is CMMG’s RipBrace. The RipBrace is an arm brace that is adjustable, but unlike regular arm braces, you can pre-set the extended length. For me and my long arms, the full length of the brace is what I need, but those with shorter arms can use the included P3 indexing screw to shorten the extended length. To open the brace, just grab and pull (hence the “rip” of RipBrace).

For a finish, the test gun came with a Sniper Gray Cerakote protective finish. A finish of this type will run you an extra $150. Cerakote is standard on the 300 Series, but they come with 5-inch barrels, so I opted for an 8-inch barrel and paid extra for the Cerakote.

The Banshee comes without sights. For our testing, I used a red-dot optic for the chronographing and drills/testing work, and I used a magnifying optic for the accuracy testing.

Recoil is further controlled by the application of a CMMG SV muzzlebrake.

The PCC Difference

The .40 S&W has gotten a certain amount of deserved flak of late. Basically, in handguns the .40 over-promised and under-delivered. It was supposed to be the near-9mm-recoiling cartridge that hit like a .45. It ended up as the near-.45 recoiling cartridge that everyone hated to qualify with.

But put that cartridge in a PCC, and all of a sudden things are different. The recoil difference between a 9mm and a .40 S&W, when you use the RDB system and a PCC, becomes no big deal. The capacity difference between 9mm and .40 becomes nothing when you get to the big stick magazines. A large Glock mag in 9mm holds 33 rounds; it holds 31 in .40.

The chrono testing and felt recoil bore that out. I shot a selection of 180-grain factory ammo out of the CMMG, and the velocities were a bit more than they would be from a handgun. That’s expected with the barrel being longer. It wasn’t as much as you might see with other cartridges simply because the .40 is already running at the max. But the felt recoil was not significantly greater than that of a 9mm PCC.


So, for a negligible amount of extra felt recoil, you get more performance. Compared to a similar 9mm, where you might be firing a 147-grain bullet, the .40 nets 33 grains more bullet weight (a 22 percent increase) and as much as 100 feet per second (fps) more velocity (10 percent more). Who doesn’t want more, especially when you don’t have to pay for it? Plus, you get accuracy, ease of handling and wicked-fast engagement.

Where in a handgun the .40 over-promises and under-delivers, in a PCC, the cartridge becomes what we were promised. You get, especially with the CMMG Banshee, a firearm that has the capacity of a 9mm, but hits like a light .45 ACP. In other words, a smokin’ hot and compact truck gun.

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