The CMMG BANSHEE MK4 5.56x45 12.5" upper group delivers compact firearm maneuverability without sacrificing the ballistic performance you'd expect from a carbine-length system. Built around a 12.5-inch barrel in 5.56mm, this upper group is designed to pair with any Mk4 or standard AR-15 lower to create a nimble AR pistol or short-barreled rifle. Whether you're building a truck gun, home-defense rig, or a versatile close-quarters platform, the BANSHEE's compact footprint makes it easy to move through tight spaces while the direct impingement operating system keeps things simple and reliable.

Everything ships complete and ready: the upper arrives with bolt carrier group installed, a CMMG ZEROED linear compensator to manage recoil and muzzle rise, an ambi charging handle for either-hand operation, and a polymer dust cover. The billet 6061-T6 aluminum upper receiver is finished in Cerakote, and the EML11 M-LOK handguard gives you a modern, lightweight platform for mounting lights, lasers, or other accessories. At just 3.8 pounds, this upper stays light enough for all-day carry while the 1:7 barrel twist stabilizes a wide range of 5.56 projectiles.

The 4140CM barrel is finished to military specs and comes with a carbine-length gas port and a fixed 0.750" non-Adjustable gas block—proven geometry that favors reliability in a short-barreled package. The 1/2x28 muzzle threads accept standard AR accessories if you want to swap the included compensator for a suppressor or different muzzle device later. This is a no-compromise, plug-and-play upper for builders who want quality parts, smart features, and genuine compact handling without the need for finicky tuning.

The CMMG BANSHEE MK4 5.56x45 12.5" upper group delivers compact firearm maneuverability without sacrificing the ballistic performance you'd expect from a carbine-length system. Built around a 12.5-inch barrel in 5.56mm, this upper group is designed to pair with any Mk4 or standard AR-15 lower to create a nimble AR pistol or short-barreled rifle. Whether you're building a truck gun, home-defense rig, or a versatile close-quarters platform, the BANSHEE's compact footprint makes it easy to move through tight spaces while the direct impingement operating system keeps things simple and reliable.

Everything ships complete and ready: the upper arrives with bolt carrier group installed, a CMMG ZEROED linear compensator to manage recoil and muzzle rise, an ambi charging handle for either-hand operation, and a polymer dust cover. The billet 6061-T6 aluminum upper receiver is finished in Cerakote, and the EML11 M-LOK handguard gives you a modern, lightweight platform for mounting lights, lasers, or other accessories. At just 3.8 pounds, this upper stays light enough for all-day carry while the 1:7 barrel twist stabilizes a wide range of 5.56 projectiles.

The 4140CM barrel is finished to military specs and comes with a carbine-length gas port and a fixed 0.750" non-Adjustable gas block—proven geometry that favors reliability in a short-barreled package. The 1/2x28 muzzle threads accept standard AR accessories if you want to swap the included compensator for a suppressor or different muzzle device later. This is a no-compromise, plug-and-play upper for builders who want quality parts, smart features, and genuine compact handling without the need for finicky tuning.