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Silencer Shop Authority: CMMG MkGs 9mm Banshee Review

Pistol caliber ARs are a dime a dozen these days. We’ve come a long way since the early-1980s Colt 9mm SMG, but the basic design of the typical 9mm AR really hasn’t changed a whole lot. For the most part, current 9mm offerings still employ simple, but bulky, straight blowback operation and Colt, Uzi, or Sten stick magazines. In short, most of the “modernization” that has graced these sub-caliber slingers has been limited to quality-of-life improvements like optics and furniture.

The folks at CMMG march to a slightly different beat. Once known as a manufacturer of high-quality, but relatively “vanilla” AR-15 rifles, CMMG’s recent offerings have been a bit more unique. It all started with the company’s efforts to perfect the .22 LR AR-15, but kicked into gear with the introduction of the CMMG Mk47 Mutant – an AR-15/AR-10 hybrid made to take AK magazines and ammo – back in 2014. in 2017, the company again expanded its lineup with the 9mm and 45 ACP Guard series of carbines and pistols that use an intriguing, but not totally new Rotary Delayed Blowback system to increase lock up time and reduce bolt velocity.

The rotary system has an interesting history. Originally designed by Ferdinand von Mannlicher in the late 1800s, it was conceived as a means to turn what was otherwise a standard bolt-action rifle into a semi-automatic carbine. This places the design as one of oldest delayed blowback systems in existence. However, early teething issues and the popularity of firearms based on other designs – particularly Volgrimmer’s roller delayed approach – left the rotary system mostly in the past. CMMG’s Guard picked up this old torch, dusted it off, and carried it into the modern era.

With this background, let me introduce the CMMG Banshee 300 Series MkGs 9mm short-barreled rifle (SBR). CMMG has taken the Guard and pushed it a little further, adding new furniture, a shorter barrel, and more ambidextrous controls. They’ve also made it a Silencer Shop exclusive. Thanks to Modern Rifleman’s partnership with Silencer Shop, I recently spent some time with this new blaster.

The Build

In terms of outward appearance, there really isn’t much about the Banshee that significantly departs from other pistol caliber ARs. It features a 7075 hardcoat anodized receiver set mated to CMMG’s 4” RML M-LOK free-float handguard. The upper receiver is forged and, at time of review, the lower was billet. It is my understanding that in 2018, CMMG swapped the billet lower for a similarly-designed forged part. The RML is very lightweight and slim enough that the included Magpul MVG is greatly appreciated. The Banshee’s pistol grip is a standard Magpul MOE.

CMMG Banshee 9mm SBR Left Red Dot
The Banshee is shown here with my 30mm Primary Arms red dot.

One of the most significant changes from the aforementioned Guard is the new RipStock low-profile collapsible stock. This thing is a solid piece. Its all-aluminum construction hearkens back to the old CAR stocks, but the RipStock supports three positions instead of the legacy stock’s two. The aluminum helps to make the RipStock very rigid, but the stock does wobble slightly on the receiver extension. While It’s not enough to seriously affect stability, the unit has an annoying rattle when shaken.

CMMG 9mm Banshee Ripstock Stock
The RipStock is a solid piece of kit, but it does rattle on the receiver extension.

Just forward of the stock, the Banshee features an ambidextrous, extended charging handle. There’s no question that the handle’s extended arms make it very easy to actuate, though I found that it had a tendency to catch on clothing and gear from time-to-time under use. I’d probably prefer a slightly lower profile handle here. Other ambidextrous additions include a new selector lever and sling loops on both sides of the receiver end plate.

Banshee 9mm CMMG Charging Handle Ambi
If you're a lefty, or otherwise a fan of extended, ambidextrous charging handles, the Banshee won't disappoint.

The Banshee’s 5” barrel is its most noteworthy upgrade (in my opinion) over the Guard. Even in pistol format, CMMG’s incumbent comes with an 8” barrel at its shortest. Shaving another 3” from the barrel length makes the Banshee extremely compact and ideal for a suppressor like CMMG’s new DefCan 9. With a barrel this short, there’s less incentive to search out the absolute most compact suppressor as just about any of the reputable options out there will keep the overall length of the barrel-plus-silencer under 16”.

CMMG Banshee 9mm RML Rail
The Banshee's short 5" barrel sits under an even shorter, 4" RML handguard.

There are two noteworthy omissions with the Banshee that I feel a firearm of this price should include – sights and a muzzle device. Neither are really a big deal, but including something like one of CMMG’s Bi-Lock mounts straight out of the box (the one pictured here came with the DefCan 9) would add value without substantially increasing CMMG’s cost. The same goes for sights. Magpul’s polymer MOE “irons” are ultra-affordable and perfectly usable. Like I said, these aren’t deal breakers. I’m just part of that group who thinks a high-end product should come with an experience to match.

CMMG Banshee 9mm Mag Release
While the charging handle and selector lever are amidextrous, the Banshee's bolt release and magazine release (shown here) are not.

The Banshee, like the Guard, uses CMMG’s fantastic Radial Delayed Blowback system. Since some readers might not be fully aware of the significance of this system, let me provide some context. Most subguns and the like use straight blowback systems. Since straight blowback guns lack any sort of locking mechanism to prevent the chamber from opening under the high pressure behind each shot, heavy bolts are often used. This increases the energy needed to open the action and sufficiently slows the firearm’s operation to maintain safe and reliable performance.

CMMG Banshee 45 Bolt Lugs AR-15
Lugs like these aren't a common sight on pistol caliber AR-15s.
CMMG Banshee 45 Radial Bolt AR-15
The chamfered back faces of the lugs are key to the radial blowback system's operation.

The Radial Delayed Blowback system is a substantial improvement upon this traditional operation. Rather than opting for an unusually heavy bolt/carrier, CMMG took elements from the AR-15’s direct impingement bolt head and adapted them to gasless operation. Preserved are the AR’s seven bolt lugs, but gone is the hollowed gas key. For the most part, the Banshee’s bolt and carrier look a lot like standard AR-15 parts, but the rear of each bolt lug is an angled, or chamfered. With the firearm in battery, the Banshee’s bolt “locks” into the barrel extension much like any normal AR. However, when the round is fired, the pressure behind the bullet presses those chamfered faces against the barrel extension, forcing the spring-loaded bolt to rotate and unlock for cycling. This rotation delays the action enough to allow chamber pressure to drop to safe levels.

Did you really think I was going to move on without answering the most important question on every readers’ mind? Since you’re already wondering (and probably have also figured out), the answer is yes, the Banshee does accept 9mm Glock magazines. I truly think I might have been the only person in the world who couldn’t have cared less about this feature prior to reviewing this SBR, but I’ve been converted. It’s no secret that I own a Zenith Firearms Z-5RS and that I love MP5 magazines for their ease of loading and durability. The included 33-round Glock magazine comes very close to matching most of the MP5 magazine’s best features and additional magazines are cheaper and more plentiful to boot.

Range Report

Prior to hitting the range with the Banshee, I had absolutely no experience with CMMG’s Radial Delayed Blowback guns. While I had seen the Guard series at SHOT and elsewhere, it wasn’t until recently that I even realized there was anything special about the guns. To me, they were just more pistol caliber ARs with a little added flair. I should have known better.

The first thing to note about the Banshee is that it is just a joy to shoot – far better than most other 9mm ARs. It has long been known that roller-delayed MP5s are superior shooters to straight blowback ARs. With respect to felt recoil and muzzle flip, the Banshee compares VERY favorably to the MP5 and totally demolishes simpler designs. The action isn’t quite as buttery smooth as the MP5, but it cycles faster (than my full-size Z-5RS) and the gun has much, much better ergonomics. If you’re looking for a viable, modern alternative to the German juggernaut, the Banshee is worth a look.

Since the Banshee unfortunately comes without sights, I decided to swap my Primary Arms Advanced 30mm Red Dot over from my Mk18 build-in-progress. The red dot performed well (unsurprisingly) as did the Banshee. I had no trouble managing half-dollar sized 25-yard groups with the rifle simply rested on its magazine. An ideal shooting platform? No, but workable nonetheless.

The interesting accuracy related data point came when I mounted CMMG’s DefCan 9 suppressor to the rifle’s pre-installed Bi-Lock mount. I noted this in my review of the silencer, but for some reason, mounting the can to the gun shifted the point of impact by nearly 8 MOA (2” at the tested 25 yards). My best efforts couldn’t uncover a reason for this. The baffles and end cap of the suppressor looked pristine and I could only guess that the long DefCan had some sort of effect on the harmonics of a firearm that was otherwise configured with a very short barrel.

While we’re talking about suppressors, it’s worth noting that the Banshee is a phenomenal host rifle. The added lock time provided by the Radial Blowback system makes all the difference here. Minimal port pop contributes to a fantastic at-ear experience for shooters the likes of which can (again) only be rivaled by the MP5 and perhaps SIG’s MPX. Even compared to the integrally-suppressed Spike’s Tactical Brown Recluse that I reviewed previously, the Banshee MkGs is a clear winner.

Conclusion

If it sounds like the Banshee MkGs won me over, it’s because the rifle did just that. I took delivery of the gun knowing relatively little about it and by the time I sent it back, was completely sold.

The efficacy of the Radial Delayed Blowback system cannot be overstated. It shoots like an MP5, but is a simpler design that requires no welds and has no need for feeler gauges to periodically check bolt gap. Combine that with the Banshee’s light weight and superior ergonomics and I’m having a difficult time finding reasons not to like the MkGs.

That said, it isn’t totally perfect. I noted odd accuracy behavior with CMMG’s DefCan 9 suppressor mounted. I tend to blame this on the silencer. The rifle’s lack of included sights was also a disappointment for a gun at this price point. Still, I feel the Banshee’s upside substantially outweighs these weaknesses.

If you’re looking to pick up one of the best 9mm carbines on the market, Silencer Shop is the exclusive distributor of the Banshee MkGs SBR. You can find it there for $1,449 sans tax stamp.

This has been a review of products provided by and sold at Silencer Shop. All opinions are my own.

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