CMMG Banshee Mk4 Review: In the Field!

by coldboremiracle

July 25, 2022



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 Banshee from CMMG, it is a nine-millimeter carbine that is a bit different than everything I’ve ever tried before.

Banshee Mk4 Specs

  • Caliber 9mm
  • Operating System Radial Delayed Blowback
  • Barrel Twist 1-10
  • Trigger Type Mil-Spec Single Stage
  • Magazine CMMG 9ARC 30RD
  • Weight 4.7lbs
  • Length 20.8″

CMMG Banshee Mk4 Background

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. The 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 breach 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 (PCCs).

More advanced designs like the MPX utilize a gas system like those seen in many AR-pattern rifles for more reliable functions. And still others like the old roller guns from HK utilize a different locking bolt and a gas-operated system for their legendary reliability.

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. The 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.

CMMG Banshee Mk4 Features

CMMG Banshee Mk4 Features
1 Radial delayed blow-back system

Allows the Banshee to use much lighter carriers than traditional blow-back designs and better controllability

2 Ripbrace “not-a-stock”

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

3 Sixty vs. ninety degree safety

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

4 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.

5 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

6 Threaded barrel and compensator

The Banshee comes with a linear compensator to reduce muzzle rise, and underneath the muzzle was threaded 1/2-28

Banshee Models or Colors

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 – Our Take

After mounting up a Sig 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 and 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 solid mass of pistol, elbows, and arm bones. I started popping off several rounds, and the bumping of this little banging Banshee felt just like I hoped it would feel. The lightweight was matched by its 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, 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 an 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.

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 because I knew it was up to the task and easily swapped out the muzzle threads to fit the Banshee. I was shooting 124-grain supersonic ammunition so I wasn’t expecting it to be extremely quiet, but it did seem to be quieter than I expected. Most of the PCCs I have shot in the past were blow-back designs but delayed guns like this Banshee seem to be quieter still due to their breach staying closed longer.


With the Romeo and the R9 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.

Banshee Mk4 Pros and Cons

  • The weight and controllability, very shootable
  • Quality at or above its price point
  • Excellent and familiar controls
  • Excellent suppressor host
  • Could use a more prominent hand hook at the front
  • Do you want to use pistol mags or AR mags?

Report Card


Lightweight and comfortable, the balance of the pistol when firing is excellent and keeps you on target.


I experienced no malfunctions while shooting the Banshee, either suppressed or otherwise. I would have preferred to test a larger variety of ammunition to confirm.


Perhaps if the Banshee was an SBR instead of using the necessarily evil brace it would be just a touch more customizable for the shooter. Keep an eye on your support hand fingers or you could lose one.


I found the Banshee to be as accurate as I could expect from any 9mm pistol or PCC. Guns of this type aren’t meant for match grade accuracy, but hitting what I expected with the Banshee was easy


While there are plenty of less expensive PCC’s or AR 9mm pistols, they do not compare to the Banshee with its technological advantages.  I’d say the Banshee is worth it’s price, it’s just a little more than most would like to spend.

CMMG Banshee Mk4 Final Grade

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Reviewed by coldboremiracle

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Based on 11 Reviews

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Banshee Mk4 Ammo 

I 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.

Box of Hornady 9mm pistol ammunition

Hornady Critical Defense 115 GR

Cost Per Round
Cabela’s $1.24
Midway USA $1.24

Magtech 115 grain 9mm

Cost Per Round
OpticsPlanet $0.39

Banshee Mk4 Starter Pack

So what’s next? Well, if you decide to get the Banshee Mk4, you’re going to need to pick up some must-have basics. Here’s our recommendation for what you need to get started.

  • Gun Cleaning Kit: Otis All Caliber Elite Range Box on Amazon or build your own personalized cleaning kit with premium components.
  • Shooting Glasses: All it takes is one piece of rogue hot brass, and you’ll learn the importance of shooting glasses. But not all glasses are built the same. See our recommendations for the Best Shooting Glasses.
  • Hearing Protection: Firing a gun without wearing proper ear protection can be very dangerous and detrimental to your hearing. Find out the best hearing protection for you in our full-length review.
  • Storage: Check out our article on the Best Biometric Gun Safes
  • Targets – If you’re wanting a great resource for shooting practice or zeroing your optics on your optics rifle or pistol, download our FREE Sighting in Targets below.

Banshee Mk4 Accessories 

I feel like the Banshee is a perfect place to use the Sig Romeo, but 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, and 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 Magpul MS1 model, the Banshee is not a heavy load to carry, but 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.

SIG Romeo5
  • 2 MOA Red-Dot
  • Motion Activated Illumination
  • Integrated M1913 Picatinny interface
Check Amazon
US Optics TSR-1X
  • 5 MOA Red Dot
  • Manual Controls
  • 12 HR Auto Shutoff
Check Amazon
Yankee Hill R9 Suppressor
  • It features 1-3/8”-24 rear mounting threads
  • Fully-welded tubeless design
  • Made from 17-4 PH Stainless Steel
Check Price
Magpul MS1 Sling
  • MS1 slider provides rapid adjustments
  • Strong and wear resistant
  • Survived testing with tens of thousands of cycles in wet, dry and sandy conditions.
Check Amazon


Not only do you need to keep your firearms safe and secure, but you’re also going to need to know how to take care of them. While scouring the internet, we came across this excellent video:

For more info regarding the Banshee Mk4, check out the following resources:


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About coldboremiracle

coldboremiracle is a self-taught "Freelance Sharpshooter" based in the Rocky Mountains. A true gun nut at heart, but has a passion for precision shooting particularly as it applies to hunting. When not at home or work, he is more than likely behind a riflescope in the high country evaluating the wind for the next shot.

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  1. Cmmg = poor quality at premium prices do not buy. They use 4140 for the barrel instead of 4150. They use cheap 6061 aluminum for the upper instead of 7075. And it is not hard anodized. The bcg is not carpenter steel. They cut corners on virtually every part of their buns and charge the same price as premium rifles.

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