The CMMG Banshee 9MM Mk4 AR Pistol


Nine millimeter carbines have become extremely popular over the last few years, and with ammo prices maintaining their ridiculous highs it should come as no surprise that people are looking for less expensive range guns. Today we are talking about the CMMG Banshee 9mm Mk4 AR pistol, it is a nine-millimeter carbine that is a bit different than everything I’ve ever tried before.

The CMMG Banshee is a nine-millimeter AR style pistol, it features a five-inch Chromoly barrel with a 1-10 twist. A pistol brace is mounted at the back on the buffer tube, and using both 6061 and 7075 alloys for the upper and lower receiver help keep the weight of this little pistol down to four-point-seven pounds.

Overall length of the pistol is just under twenty-one inches, making the Banshee Mk4 a very mobile and handy weapon. Other features such as custom furniture and six different Cerakote colors to choose from put the Banshee on many shooters want list.

Many of the nine-millimeter carbines on the market today are of the blowback type. This simple design operates much like a semi-auto pistol.  Utilizing the recoil and pressure generated at the breech of the barrel to open and cycle the action.

It is less expensive and requires fewer parts in most cases which makes it a good option for entry-level priced pistol caliber carbines (PCC’s).
More advanced designs like the MPX utilize a gas system like those seen in many AR pattern rifles for more reliable function. And still others like the old roller guns from HK utilize a different locking bolt and a gas-operated system for their legendary reliability.

What makes the Banshee scream?

The Banshee utilizes CMMG’s Radial Delayed Blowback system to improve several aspects of the carbine. One of the many complaints with blowback systems is the heavyweight that is typically required to hold back the bolt long enough for the bullet to get down the barrel. Heavy bolts made from blocks of steel are usually the culprit.

Another of the complaints heard about blowback-operated guns is the recoil impulse felt by the shooter. With nothing holding the bolt closed but its weight and spring pressure, a blowback gun begins moving and opening the action as soon as the shot is fired. This added to the heavy cyclic weight of the bolt increases the feeling of recoil and motion.

More advanced designs of the gas-operated systems don’t start operating the action until the bullet has left or nearly left the muzzle. And with their lighter bolt carriers they feel much smoother in operation.

The radial delayed system of the Banshee allows greater reliability than traditional blow-back designs. It also makes the weapon more stable and controllable by reducing the recoil impulse with its lighter bolt carrier group.

The Banshee

The CMMG Banshee has several features that will make it extremely popular for AR-style rifle enthusiasts.

-Radial delayed blow-back system. The flagship feature of the Banshee series of rifles is the CMMG’s patented radially delayed system. The beveled lugs on both the bolt and barrel extension cause the bolt to be pushed open as it pivots inside the carrier, the time it takes to rotate the bolt out of battery allows chamber pressures to drop to much lower pressures before opening. This feature also allows the Banshee to use much lighter carriers than traditional blow-back designs.

-Ripbrace “not-a-stock”. The pistol brace that comes with the Banshee has several locking points that are locked into position using the common rocker lever under the “stock”. The difference between this one and others is that the Ripbrace has beveled pin bosses in the rear-pulling direction. This allows the stock to be pulled as far to the rear as the user would like without the need to push any release rocker. It makes for fast and simple deployment of the weapon.

-Threaded barrel and compensator. The Banshee comes with a linear compensator to reduce muzzle rise, and underneath the muzzle was threaded 1/2-28. This is a must nowadays, as suppressor have become extremely popular.

-Standard AR mags with adaptor. The Banshee Mk4 utilizes standard AR 5.56 sized magazines. The 9mm cartridges are made to fit using a magazine insert that uses its own internal feed ramp and follower.


-Sixty vs. ninety degree safety. Most AR’s can take a an ambidextrous safety, but the ambidextrous safety provided by CMMG has a reversible center barrel that allows you to choose either sixty or ninety degrees of motion to safe or fire the weapon.

-Ambi mag catch. Magazine catch controls are located on both sides of the receiver, allowing ambidextrous control of the magwell and it’s contents.

-Extended mag release. The Banshee comes standard with extended magazine release buttons, I found them more than adequate and added ease when dropping the magazine.

CMMG has offered a wide selection of configurations for the Banshee. Including six different Cerakote colors; black, green, tan, bronze, grey, and titanium. The Mk9 series of Banshee utilizes pistol magazines, but that’s for another story.

On the range with the CMMG Banshee

After mounting up a Sig Sauer Romeo on top of the Banshee, and grabbing a few accessories for it, I headed out the door with great expectations. I don’t much care for proper ranges, and I avoid them as best I can. So into the mountains I fled with a Banshee under my arm.
I began loading the curious magazine, which was much easier than I had anticipated. The inner mag adaptor has feed lips that mate to the existing P-mag feed lips, the front of the magazine adaptor is a long feed ramp. Stuffing thirty rounds into the magazine went quick, and it was time to empty it.
Shouldering this tiny little pistol felt so easy. The lightweight and size of it make you almost ball up into a a solid mass of pistol, elbows and arms bones. I started popping off several rounds, and the bumping of this little banging Banshee felt like just like I hoped it would feel.

Light weight was matched by the CMMG Banshee’s light recoil, and before I knew it I was back to fumbling fresh cartridges into the magazines. I made a few adjustments to my Romeo, and went right back to shooting. The linear compensator wasn’t particularly noticeable. It’s hard to say how much of a difference it made with such light recoil anyway.

My nine year old had come along with me, and as kids often do he started hinting at interest in shooting the Banshee. He’s shot plenty of other guns so this wasn’t a big ask, but I was supremely pleased as I watched how simple it was for him to handle and manipulate the gun. I collapsed the brace to better fit his little stature and off he went.

Shop all the Banshee model here

Shooting the CMMG Banshee Suppressed

Since I am not one for making a racket, so it was time to see how this pistol would do suppressed. I had brought along my Yankee Hill Machine R9 suppressor.  I knew it was up to the task and easily swapped out the muzzle threads to fit the Banshee.

Shooting 124 grain supersonic ammunition I wasn’t expecting it to be extremely quiet, but it did seem to be quieter than I expected. Most of the PCC’s I have shot in the past were blow-back designs.  Delayed guns like this Banshee seem to be quieter still due to their breech staying closed longer.

The Banshee with the Romeo red dot and the YHM R9 suppressor

With the Romeo and the YHM R9 suppressor installed, we spent a good portion of the day making little piles of brass all over. I’m not sure what kind of accuracy you might expect from a 9mm carbine such as this. But hitting things like soda cans and six inch steel plates at fifty-yards seemed pretty easy. I would have liked to try some different ammunition in the gun to see if it had a preference for one over another. But the way things are at the gun counter right now I was lucky to get what I could.

Pros and Cons

There are quite a few pros when it comes to the CMMG Banshee, many of which I’ve already mentioned above. For me, the best pros of the Banshee are the weight and controllability. It almost felt like a toy compared to a CZ Scorpion or an MP5.  It was easy to control with almost zero muzzle rise when suppressed.

The quality of the Banshee felt at or above its price point, with smooth fit and sexy finish. And all the little things like the extended mag buttons and such made this rifle feel perfect in my hands.

I suppose there are a couple things that I could call cons, but I’m not sure they can be blamed on the Banshee’s design alone. Short guns like this can be more than a little handy.  But if you aren’t careful with your hand, you may find it has some new holes in it.

CMMG put a good little hook at the front of the handguard to keep you from getting your fingers to close to the muzzle.  It is still close enough that a careless move could cost a finger though. This is of little concern to me as I will probably always use a suppressor on the gun. I’m still unsure if I would prefer the Mk9 Banshee over the need to put adaptors in several P-mags, but that is another thing to evaluate. Continue Reading Here…

Ammo Used with the Banshee

We shot quite a bit of 124 grain Hughes Precision ammunition through the Banshee, and it seemed to love every bit of it. I also shot some Magtech 115 grain ammo through it that also performed flawlessly.

If I had my choice I would stick with the heavier loads. I would even prefer some heavy sub-sonic ammunition to shoot the Banshee suppressed. The delayed operating system would be ideal for super quiet subs when used with a suppressor.


I feel like the Banshee is a perfect place to use the Sig Romeo.  I also used the US Optics TSR-1X which also was a good match for the Banshee. The suppressor was an absolute must-have for me. The R9 from Yankee hill was a great match for compact and quiet shooting.

Another great option to add to the Banshee is a good sling like the padded Magpul MS1 model.  Since the Banshee is not a heavy load to carry,  having a good sling to drop the gun in favor of a secondary weapon is a good option. I suppose the only other thing I would add to the Banshee is a good set of backup sights. I like the Magpul MBUS Pro’s for this purpose.

The Banshee functions like a standard AR-15


CMMG’s Banshee is an outstanding little AR pistol. It runs flawlessly and bring comfortable easy shooting to an extremely compact firearm. Simple and convenient operation as well as the magazine situation make the Banshee and excellent traing tool as well.

While it may be a touch expensive for a little 9mm pistol. I think it is well worth the price. Tell us what you think of the Banshee below!


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