The CMMG Banshee MK4 5.7x28mm, model 54A3B0FMB (UPC 810148624194) is a compact, AR-pattern pistol configuration built around the 5.7x28mm cartridge, with a 5" black nitride medium-taper threaded barrel, 40+1 capacity, and a Midnight Bronze Cerakote aluminum receiver. This configuration also features M-LOK handguards, a full-length Picatinny rail receiver, and CMMG Zeroed™ grips, forming a compact 5.7x28mm platform with modern furniture and modular mounting options.
Platform and Caliber
This Banshee MK4 variant is chambered in 5.7x28mm, a small-caliber, high-velocity cartridge originally developed for compact firearms:
Caliber: 5.7x28mm
Standard capacity (magazine-dependent): 40 rounds, with a total listed capacity of 40+1 when a round is chambered
Operating system: AR-15–style layout using CMMG’s MK4 configuration, designed around standard AR-style controls
The 5.7x28mm chambering allows for lightweight ammunition and typically low felt recoil relative to many traditional rifle cartridges, supporting faster follow-up shots when used within its design envelope and in accordance with all applicable laws and safe handling practices.
Barrel and Muzzle Configuration
The heart of this model is a 5" medium-taper barrel finished in black nitride:
Barrel length: 5 inches
Profile: Medium taper
Finish: Black nitride, chosen for surface hardness and corrosion resistance on the steel barrel
Muzzle: Factory threaded to accept compatible muzzle devices (such as compensators, flash hiders, or other accessories designed for the correct thread pitch and caliber, where lawful)
A 5" barrel keeps overall length compact while maintaining a true 5.7x28mm chamber, making this configuration suited for close-range use and transport where a shorter form factor is desired.
Receiver and Finish
This model uses an aluminum receiver set with a distinct Midnight Bronze Cerakote finish:
Receiver material: Aluminum (upper and lower receiver set, AR-style)
Finish: Midnight Bronze Cerakote, a baked-on ceramic coating designed to provide abrasion and corrosion resistance while adding a distinctive bronze tone
Configuration: AR-15–style MK4 pattern with forward assist, shell deflector, and top rail integration (configuration may vary slightly by specific production run)
Cerakote is applied as a protective and cosmetic finish; Midnight Bronze gives this Banshee MK4 a darker, earth-tone metallic appearance contrasted against the black barrel, handguard, and furniture.
Handguard and Mounting Interfaces
The M-LOK handguard and Picatinny rail receiver provide flexible mounting options:
Handguard type: Free-float style with M-LOK slots for attaching compatible accessories such as vertical grips, hand stops, lights, or sling mounts
Top rail: The receiver integrates a Picatinny (MIL-STD-1913) rail, allowing mounting of:
The combination of M-LOK on the handguard and Picatinny on the upper receiver supports modern accessory mounting standards widely used across AR-pattern firearms.
Controls, Furniture, and Grip
The CMMG Banshee MK4 5.7x28mm retains familiar AR-style controls with upgraded furniture:
Controls:
Grip: CMMG Zeroed™ grip, designed with modern ergonomics for a full firing-hand purchase and texturing intended to enhance control
Brace/Rear configuration: Depending on jurisdiction and current regulations, the rear of the firearm may be configured as a pistol tube, buffer system, or other compliant rear assembly as specified at the time of sale (details vary by configuration and evolving rules; always verify your specific model and local law)
The Zeroed grip and AR-style control layout allow users familiar with the AR platform to transition with minimal retraining, while still benefiting from the compact 5.7x28mm format.
Capacity and Magazine System
This variant is configured for 40-round magazines in 5.7x28mm:
Capacity: 40+1 (forty-round magazine plus one round in the chamber, when loaded to that condition in accordance with safe handling practices)
Magazine type: Detachable box magazine, sized for 5.7x28mm
Compatibility: Designed around CMMG’s 5.7x28mm magazine system for the MK4 platform; actual magazine compatibility and availability may vary and should be confirmed with manufacturer specifications
As with any firearm, users must ensure that magazine capacity complies with all local and state regulations in their jurisdiction.
Rail and Accessory Options
Thanks to the Picatinny receiver rail and M-LOK handguard, the CMMG Banshee MK4 5.7x28mm can be configured with a variety of accessories (where legal and appropriate):
Optics: red dot sights, compact prism optics, or similar sighting systems
Backup sights: folding or fixed iron sights mounted on Picatinny sections
Illumination and aiming: weapon lights or laser devices designed for M-LOK or Picatinny mounting
Ergonomic accessories: hand stops, foregrips, or sling attachments compatible with M-LOK
Any accessory installation should follow manufacturer torque and mounting guidelines and remain compliant with laws governing firearm configuration in your area.
General Use and Configuration Context (Technical)
In general technical terms, a compact 5.7x28mm AR-pattern pistol like the Banshee MK4 54A3B0FMB is often configured for:
Controlled, close-range shooting in environments where a shorter overall length is beneficial
Range use and training with low-recoil 5.7x28mm ammunition
Applications where modular mounting of optics and accessories on M-LOK and Picatinny surfaces is desired
Actual configuration and intended lawful use should always be aligned with applicable federal, state, and local regulations, as well as safe handling standards.
Safety and Responsible Use
For any firearm, including the CMMG Banshee MK4 5.7x28mm, safe and lawful operation is essential:
Always treat every firearm as if it is loaded.
Keep the muzzle pointed in a safe direction at all times.
Keep your finger off the trigger until your sights are on target and you have made the decision to fire.
Be sure of your target and what is beyond it.
Use only clean, undamaged ammunition that matches the firearm’s marked caliber (5.7x28mm).
Follow CMMG’s published guidelines for maintenance, cleaning, and inspection of the barrel, receiver, and moving parts.
Any modifications or changes to the firearm should be performed by qualified individuals and must remain in compliance with all applicable laws.
This technical description of the CMMG Banshee MK4 5.7x28mm 40+1 with 5" black nitride medium-taper threaded barrel, M-LOK handguards, Midnight Bronze Cerakote aluminum receiver, Picatinny rail, and CMMG Zeroed grip (model 54A3B0FMB, UPC 810148624194) is intended to outline its main construction details, features, and configuration so you can clearly understand the components and layout of this specific 5.7x28mm AR-pattern platform.
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