The CMMG Banshee MK4 Upper Group (brand part number 55BDFF4AB) pairs a 12.5-inch 5.56x45mm barrel with the Mk4 platform for a compact AR pistol or SBR build that keeps carbine-like ballistic performance. Built by CMMG, this Direct Impingement upper works with any standard AR15 or Mk4 lower group and 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 linear compensator, all finished in Cerakote.

Key Specifications

• Chambered in 5.56x45mm on the Mk4 platform.
• Barrel length is 12.5 inches.
• Operating system is direct impingement.
• Twist rate is 1:7, matched to a wide range of 5.56 bullet weights.
• Barrel material is 4140 chromoly steel with a salt bath nitride finish.

Frequently Asked Questions

Does this upper include a bolt carrier group? Yes, all CMMG Upper Groups ship complete with a bolt carrier group and CMMG’s ZEROED accessories.

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 MK4 5.56×45 12.5-inch Upper

Blend maneuverability with carbine-like performance in one compact upper group. Order this AR-15 upper from our Lubbock, Texas gun shop for fast, insured shipping to your door.