The CMMG Banshee Upper Group (brand part number 57BBCF0AB) brings 5.7x28mm, a caliber gaining ground as a flat-shooting, low-recoil personal defense round, to the AR platform in a highly compact package. Built by CMMG with a 5-inch barrel, this is the most compact 5.7x28mm upper group the company offers, using a radial delayed blowback operating system designed to work with CMMG Mk57 lowers or standard AR15/Mk4 lowers when paired with 5.7 AR Conversion Mags. It ships complete with a bolt carrier group and CMMG’s ZEROED accessories, including a polymer dust cover, an ambidextrous charging handle, and a 5.56mm-pattern linear compensator, all finished in Cerakote.

Key Specifications

• Chambered in 5.7x28mm for a flat-shooting, low-recoil round.
• Barrel length is 5 inches, the most compact 5.7x28mm option CMMG offers.
• Operating system is radial delayed blowback.
• Twist rate is 1:9, matched to 5.7x28mm bullet weights.
• Barrel material is 4140 chromoly steel with a salt bath nitride finish.
• Muzzle device is a CMMG ZEROED linear compensator, threaded 1/2×28.
• Upper receiver is billet 6061-T6 aluminum with an EML4 M-LOK handguard.
• Works with CMMG Mk57 lowers or standard AR15/Mk4 lowers with 5.7 conversion mags.
• Includes a CMMG ZEROED ambidextrous charging handle and bolt carrier group.
• Overall length is approximately 13.8 inches, weighing 2.5 pounds.

Frequently Asked Questions

Does this fit a standard AR15 lower? Yes, it works with CMMG Mk57 lowers or a standard AR15/Mk4 lower when used with 5.7 AR Conversion Mags.

Can this create an SBR if I add a lower? Because the barrel is under 16 inches, pairing it with a shouldered rifle-configured lower without an approved NFA registration would create a Short-Barreled Rifle; building it as an AR pistol on an unregistered lower is legal.

Buy the CMMG Banshee 5.7x28mm Upper Group

Add a flat-shooting, low-recoil personal defense caliber to your AR lineup. Order this AR-15 upper from our Lubbock, Texas gun shop for fast, insured shipping to your door.