CMMG Banshee Mk57

CMMG Banshee Mk57

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  • Design Features
  • Build Quality
  • Recoil
  • Fun Factor
4.1/5Overall Score
  • Caliber: 5.7x28mm
  • Weight: 5.2 lbs
  • Barrel Length: 8"
  • Operating: Radial Delayed Blowback
  • Smooth Shooting
  • High Build Quality
  • High Price Point

I’m a big, big fan of the 5.7x28mm round so much so that I have penned articles about the best 5.7 guns and every 5.7 x 28 mm pistol in modern production.

So when the opportunity presented itself to test and shoot a CMMG Banshee Mk57 firsthand, I couldn’t pass it up.

What is the CMMG Banshee Mk57?

The Mk57 BANSHEE is a personal defense firearm chambered in 5.7x28mm with an 8-inch barrel, designed to optimize the performance of the 5.7x28mm round. It is built on the Mk57 platform and accepts FN Five-seveN pattern magazines featuring an oversized magazine release.

The design maintains standard AR functionalities, including a last-round bolt hold open feature. The BANSHEE series offers various cerakote finishes and includes a handguard with M-LOK slots for accessory attachments.

Ergonomics & Firearm Overview

I’ve done quite a few of the CMMG firearms, all of which I’ve been pretty impressed with.

They tend to go above and beyond on ergonomics, unique features, and calibers. They try to fill a niche that no one else is filling and put their design stamp on it while they are at it.

So, let’s jump in.


The safety on the Banshee is ambidextrous and it’s also about a 60-degree throw, which I like the 60-degree throws more than the 90s, because of the shorter travel and also overall easier to use.

cmmg banshee mk57 safety best

This one has about the same length of safety selector lever on both sides, but the right-hand side selector is a little bit thinner.

Pistol Grip

CMMG has made its own pistol grip, which has a very unique pattern. It doesn’t have a lot of tackiness to it.

cmmg banshee mk57 pistol grip

So there’s not a lot of grip. It’s kind of slick actually, with little abrasion to stop your hand from moving.

The bottom of it is similar to Magpul grip designs where it has an opening container and it locks with a little lever, but it’s also on a pivoting system so you won’t drop it and lose it, which is convenient.

Magazine Release

The magazine release is not ambidextrous. It’s only on the right-hand side and very much mimics the standard AR magazine release, with the exception of the fact that it has a massive paddle.

cmmg banshee mk57 magazine release best

It is so easy to hit this and drop the mag. It is very, very easy to use. It also has a unique design that goes into the mag well that releases it.

I believe its design mostly has to do with the magazine catch on the magazines, so it can grab the 5.7×28 mags.

Magazine Well

The magazine well is kind of CMMG’s standard flared magazine well, and does have two notches in it to where the magazine funnels. This uses the standard FN Five Seven magazine.

cmmg banshee mk57 mag well

Overall, that’s probably a good bet. However, with Smith and Wesson, Palmetto State Armory, and Ruger all making 5.7s, it might be time to look around.

However, this gun has been out a bit longer than all those, so it’s kind of hard to blame them for going the FN magazine route.

Bolt Release/Hold open

Once again, this is not an ambidextrous feature.

The bolt release and bolt hold open is standard CMMG. Does work well.

Mk57 Bolt Release

I’ve got the bolt locked to the rear while I’m writing this, and it is very easy to send into battery with the enlarged paddle.

Overall, it works well. It’s your standard AR release, but the paddles are uniquely designed. But I’ve seen this similar style on other AR-15 rifles.

Charging Handle

CMMG makes its charging handle. It’s very nice. It does have a two-claw design, and no matter which side you pull on, it will work.

cmmg banshee mk57 charging handle

It kind of resembles the Geisseles and the Radian Raptors, but it’s not those, and it’s not the Radians rebranded for CMMG.

I do believe CMMG probably makes these themselves.

Overall, it functionally works well. They are very wide, so they’re easy to grab whether you’re just wearing gloves or have something in your hand.


The trigger, I don’t know if CMMG did anything special with this, but I’ve got to be honest, it feels just kind of mil-spec.

There’s no take-up, it doesn’t appear to be a two-stage trigger. It’s just a standard run-of-the-mill mil-spec.

Works well. It shot well, so that’s all that matters at the end of the day, but there is nothing to write home about on the trigger.

Stock Options

This has the SB Tactical Brace CMMG sells it with the brace and just the buffer tube. You can’t buy this gun as an SBR as of this writing.

cmmg banshee mk57 stock

Either way, you could form one this. But you can get the buffer list or the buffer tube with nothing on it if you need to go that route.

Muzzle Device

Now, the muzzle device is unique to Mk47. It has little wrench slats on the side, and the front is just a unique design, as you can see in the picture below. Not much to say about it. It does its job.

Doesn’t mitigate recoil in any sense of the word. It’s just there for aesthetics.

CMMG Mk57 Ammo

The gold standard of 5.7 ammo has long been the FN blue tip but there are other good options on the market now, namely the ACC 5.7x28mm ammo.

cmmg banshee mk57 ammo

Shooting the CMMG Banshee Mk57

Shooting the Mk57 is fantastic. Virtually no recoil, but it still packs a nice little punch. I enjoyed shooting this gun and the fit, look, and finish.

But talking about shooting it isn’t nearly as good as seeing it being shot, so without further ado, here’s the shooting video.

CMMG Mk57 Final Thoughts

No one can take away the build quality or the shootability of the CMMG Mk57. It’s very well built and even has an extremely smooth shooting experience. But I have one critique.

This is a large gun for a 5.7x28mm round. If you look at other similar guns like the FN PS90 and the Plethora of handguns that shoot the 5.7x28mm round, you’re losing all the upside of having a nice compact gun to shoot 5.7 out of.

You might be trying to hit the comment section now and say, “But, but, the PS90 isn’t small.” and you’d be right, but what the PS90 brings to the table for its size is a 50-round compact magazine.

So, while everything about this gun is nice and shoots fantastic, I have some questions about the niche it fills.

Either way, if you want a good truck gun or a fun gun, have this gun check those boxes every day and twice on Sunday-gunday.

cmmg banshee 57


Caliber: 5.7x28mm
Barrel Length: 8″
Weight: 5.2 lbs
Price Check: PSA | Grab-A-Gun |
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Michael Savage
Michael Savage

Michael is the President of Lynx Defense and an avid gun owner and outdoors man. He's passionate about helping find the best bang for your buck and helping others learn about firearms and the industry as a whole.

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One comment

  1. All though the PS90 gives you 50 rounds, the learning curve of that rifle is worlds different than the most popular platform used today, the AR15. I don’t think round capacity should be considered over usability………just saying.

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