The CMMG Banshee Mk57 is a pistol-configuration AR-pattern firearm chambered in 5.7x28mm with an 8-inch barrel. It ships with an SBA3 pistol brace and a 20-round magazine. The finish is Sniper Gray. 
 

Key Specifications 

• Brand: CMMG 
• Model: Banshee Mk57 
• Caliber: 5.7x28mm 
• Action: Semi Auto 
• Capacity: 20 rounds 
• Barrel Length: 8 inches 
• Color/Finish: Sniper Gray 
   

Detailed Features 

• 8-inch barrel in a pistol-tube configuration 
• Chambered in 5.7x28mm 
• SBA3 pistol brace included 
• Ships with 20-round magazine 
• Sniper Gray finish throughout

The Banshee Mk57 occupies a specific niche: 5.7x28mm in a compact AR-pistol format. Owners who chose it specifically for the cartridge appreciate the light recoil and the 20-round magazine capacity. The SBA3 brace was a common positive at time of purchase, though regulatory changes around braced pistols have made some owners reconsider their configuration.

The Mk57's build quality matches what CMMG delivers across the Banshee line. The Sniper Gray finish is a practical choice that shows less wear than black. A common point of friction is ammunition cost and availability for 5.7x28mm compared to more common pistol calibers, which affects how freely owners run the platform.

Value perception depends heavily on how much a buyer values the 5.7x28mm chambering. Those committed to the cartridge find the Banshee Mk57 a well-executed package. Buyers on the fence about the caliber sometimes wish they had gone with a 9mm Banshee variant instead, given the wider ammo availability and lower cost per round.