CMMG Banshee Mk4 AR Upper .338 ARC | 10.5″ Barrel

The CMMG Banshee Mk4 AR-15 upper group in .338 ARC pairs a compact 10.5″ barrel with CMMG’s Mk4 billet receiver and EML9 handguard to create a short, serviceable AR-15 upper assembly. It uses the same bolt as 6.5 Grendel platforms and a 1:8 twist to support a range of .338 projectiles, and comes configured with a CMMG ZEROED linear compensator and 5/8×24 muzzle threads. This upper is intended to offer straightforward parts compatibility on Mk4-style AR-15 builds.

Product Specifications

• The platform is Mk4.
• The caliber is .338 ARC.
• The operating system is Compact Action-Direct Impingement.
• The barrel length is 10.5 inches.
• The barrel twist rate is 1:8.
• The barrel contour is MT.
• The barrel material and finish are 4140CM with a nitride finish.
• The muzzle device is a CMMG ZEROED Linear Compensator.
• The muzzle thread is 5/8 x 24.
• The gas block is a non-adjustable 0.750″ gas block.
• The upper receiver is Mk4 billet 6061 T6 aluminum.
• The hand guard is EML9.
• The finish is Cerakote.
• The charging handle is a Dissent side charger.
• The UPC is 840442506247.

This upper is suited to short-barrel AR-15 builds where a compact, heavier-bore option is desired and for users who reload or run mixed suppressed/unsuppressed setups that benefit from the .338 ARC’s broader velocity envelope. Its Mk4 billet receiver and EML9 handguard provide a solid foundation for sighting and accessory mounting while maintaining a compact profile.