CMMG Banshee MK4 5.7x28mm 5in Pistol, 32rd

About this product

The CMMG Banshee MK4 5.7x28mm 5in Pistol is a compact AR-pattern firearm built on a forged 7075-T6 lower and employing a proprietary radial delayed blowback system to tame the high-pressure 5.7x28mm cartridge in a 5-inch barrel configuration. This pistol falls squarely into the category of a 'firearm' under federal Title I regulations, not a pistol brace-equipped 'short-barreled rifle' under Title II—a critical distinction for compliance-conscious shooters. It ships from CMMG with their RipBrace attached, which you should treat as a cheek-weld stock alternative unless you've filed a Form 1 with the ATF for SBR configuration.

What is the CMMG Banshee MK4 5.7x28mm pistol used for?

The CMMG Banshee MK4 is for close-quarters defensive use, vehicle-based kits, or as a compact ballistic trainer where standard 5.56mm AR platforms are over-penetration concerns. The 5.7x28mm cartridge, when loaded with the proper defensive projectiles like FN SS190 or its commercial equivalents, offers reduced barrier penetration compared to 5.56mm while maintaining flat trajectory inside 100 yards. Its 5-inch barrel and overall length of just over 23 inches make it exceptionally maneuverable in tight spaces, and the 32-round magazine capacity provides substantial on-board ammunition without the bulk of a rifle-caliber counterpart.

How does the CMMG Banshee MK4 compare to a FN PS90?

The CMMG Banshee MK4 offers a more conventional AR-control layout and aftermarket compatibility than the bullpup FN PS90, at the cost of a longer overall length for a given barrel length. The Banshee uses a standard AR-15 lower receiver geometry and common Mil-Spec trigger groups, allowing users to drop in upgrades from Geissele or Timney without modification, whereas the PS90 requires proprietary trigger packs and has a distinct learning curve for its reloading procedure. For a shooter already proficient with the AR platform, the Banshee presents a lower training overhead, though the PS90's 16-inch barrel in a bullpup configuration yields higher muzzle velocity in a package roughly the same overall length as the Banshee's 5-inch pistol.

What does it weigh and what are the dimensions?

The unloaded Banshee MK4 in this configuration weighs 4.7 pounds (2.13 kg), and measures 23.25 inches in overall length with the RipBrace extended. The 5-inch barrel has a 1:9 twist rate, optimized for stabilizing the 40-grain projectiles common to the 5.7x28mm cartridge, and the handguard provides 11.5 inches of continuous M-LOK real estate for mounting lights, lasers, or vertical grips—though ATF compliance on that last item again hinges on your specific firearm classification. Its compact profile, especially when paired with a suppressor using the 1/2x28 threaded muzzle, makes it a candidate for discreet storage in a vehicle safe like a Console Vault.

Who is this NOT for?

This pistol is not for the budget-conscious shooter seeking plinking ammunition, nor for someone unfamiliar with NFA regulations surrounding pistol braces and vertical foregrips. Commercially available 5.7x28mm ammunition runs between $0.60 and $1.20 per round—significantly higher than 9mm or .223 Remington—making high-volume practice cost-prohibitive. Furthermore, attaching a vertical foregrip to a pistol under 26 inches in overall length creates an 'Any Other Weapon' (AOW) under the NFA, requiring a tax stamp; ignorance of this nuance is a felony, so if you're not prepared to navigate those rules, consider a standard rifle like the Stevens 334 in .308 Win instead.

What's in the box?

You receive the complete Banshee MK4 pistol with the RipBrace installed, one 32-round CMMG 5.7x28mm stainless steel magazine, a CMMG ZEROED linear compensator threaded 1/2x28, and the owner's manual outlining the radial delayed blowback system's maintenance schedule. CMMG does not include a case, optic, or sling, so budget an additional $300-$600 for a quality red dot like an Aimpoint ACRO P-2 and a single-point sling compatible with the QD sockets on the receiver. The manual explicitly warns against using rimfire cleaning solvents on the bolt face, as they can degrade the proprietary delayed-blowback component seals.

Is the CMMG Banshee MK4 worth it at $1,623.99?

Yes, at $1,623.99, the Banshee MK4 justifies its price for shooters who need a compact, low-recoiling defensive tool with high capacity and are willing to invest in the 5.7x28mm ecosystem. The radial delayed blowback system is a genuine engineering advantage over simple blowback 9mm AR-pistols, cutting felt recoil by an estimated 30% and prolonging component life—a system you're paying a premium to own. If your use case is simply range fun or hunting varmints, a traditional AR-15 in .223 Wylde or a shotgun like the Stevens 555 Sporting O/U will offer far cheaper per-shot costs and fewer regulatory headaches.