The CMMG Banshee Mk4 AR-15 upper group pairs the Mk4 platform with .338 ARC capability in a compact 10.5-inch barrel configuration. It uses the same bolt as 6.5 Grendel to maximize parts compatibility and features a 1:8 twist rate suited to traditional .338 projectile construction. The assembly includes a CMMG ZEROED linear compensator, an EML9 hand guard, and a Mk4 billet 6061-T6 upper receiver finished in Cerakote over a 4140CM nitride barrel. This upper is intended for short-barrel AR builds where a larger-bore cartridge and reliable direct-impingement operation are desired.
Key Specifications
- The platform is Mk4.
- The caliber is .338 ARC.
- The operating system is Compact Action–Direct Impingement.
- The barrel measures 10.5 inches for compact handling.
- The barrel twist rate is 1:8.
- The barrel material and finish are 4140CM with a nitride finish.
- The muzzle device is a CMMG ZEROED Linear Compensator.
- The muzzle is threaded 5/8″-24.
- The upper receiver is a Mk4 billet 6061-T6 aluminum design.
- The listed weight is 3.1 lbs.
Built with a billet receiver, modular EML9 hand guard, and robust barrel materials, this upper offers a practical route to integrating .338 ARC into an AR-15 platform. Its compact 10.5-inch profile and component selection provide a balance of handling and terminal energy for applications that require a larger-bore option in a short-barrel package.
