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CMMG
The CMMG Banshee Mk4 AR-15 upper group in .338 ARC brings modern large-bore stopping power to the proven AR platform without the complexity that usually comes with it. Built around the .338 ARC cartridge, this 10.5" barreled upper pairs the energy and effectiveness of a serious intermediate rifle round with the same bolt compatibility as 6.5 Grendel builds, so if you're already running that caliber, you've got half the headstart. What sets .338 ARC apart is its practical versatility: it'll run suppressed or unsuppressed without the finicky gas system tweaking that haunts .300 BLK builds, and it does both jobs with more energy downrange. Whether you're building a compact truck gun, a quiet precision platform, or a short-range thumper that doesn't need a rifle-length receiver, this upper delivers serious capability in a handy package.
The Banshee Mk4 upper is purpose-built for that balance. You get a 4140CM nitride barrel with a 1:8 twist—a slower rate that lets you work with traditional .338 caliber bullet designs if you're a handloader, giving you real flexibility in loading development. The non-adjustable gas block and direct impingement system keep things simple, and CMMG's ZEROED linear compensator handles muzzle rise while keeping things quiet and cool. The billet aluminum receiver and EML9 handguard in Cerakote are ready for hard use, and at 3.1 pounds, this is a legitimate featherweight for an upper of this capability.
This is a complete upper group—receiver, barrel, gas block, handguard, charging handle, and compensator all assembled and ready to drop onto any compatible lower. No guessing, no missing pieces, no hours of fitting and tuning. If you reload, hunt at intermediate ranges, run suppressors, or just want the punch of a real .338 in a modern rifle platform, the Banshee Mk4 gives you the parts and the platform to make it happen.
| Caliber | .338 ARC |
| Platform | Mk4 |
| Barrel Length | 10.5" |
| Barrel Twist | 1:8 |
| Barrel Material | 4140CM, Nitride Finish |
| Barrel Contour | MT |
| Upper Receiver | Mk4 Billet 6061 T6 Aluminum |
| Handguard | EML9, Cerakote Finish |
| Gas System | Compact Action-Direct Impingement |
| Gas Block | Non-Adjustable, 0.750" |
| Muzzle Device | CMMG ZEROED Linear Compensator |
| Muzzle Thread | 5/8 x 24 |
| Charging Handle | Dissent Side Charger |
| Weight | 3.1 lbs |
| Finish | Black Cerakote |
This is a Mk4 platform upper, so it's compatible with any Mk4-pattern lower receiver. Since it's built on standard AR-15 dimensions and geometry, it'll pair with any quality Mk4 lower you choose.
Yes. The .338 ARC is designed to use the same bolt as 6.5 Grendel AR-15s, so if you already have a Grendel build or bolt, you don't need to duplicate that part.
Yes. The .338 ARC is engineered to run reliably both suppressed and unsuppressed without the gas system tuning headaches that come with other large-bore AR rounds. The non-adjustable gas block is tuned to handle both configurations.
The 1:8 twist is slower than typical modern AR barrels, which allows you to use traditional .338 caliber bullet designs if you're a handloader. This gives you more flexibility in bullet selection and load development.
CMMG
The CMMG Banshee Mk4 AR-15 upper group in .338 ARC brings modern large-bore stopping power to the proven AR platform without the complexity that usually comes with it. Built around the .338 ARC cartridge, this 10.5" barreled upper pairs the energy and effectiveness of a serious intermediate rifle round with the same bolt compatibility as 6.5 Grendel builds, so if you're already running that caliber, you've got half the headstart. What sets .338 ARC apart is its practical versatility: it'll run suppressed or unsuppressed without the finicky gas system tweaking that haunts .300 BLK builds, and it does both jobs with more energy downrange. Whether you're building a compact truck gun, a quiet precision platform, or a short-range thumper that doesn't need a rifle-length receiver, this upper delivers serious capability in a handy package.
The Banshee Mk4 upper is purpose-built for that balance. You get a 4140CM nitride barrel with a 1:8 twist—a slower rate that lets you work with traditional .338 caliber bullet designs if you're a handloader, giving you real flexibility in loading development. The non-adjustable gas block and direct impingement system keep things simple, and CMMG's ZEROED linear compensator handles muzzle rise while keeping things quiet and cool. The billet aluminum receiver and EML9 handguard in Cerakote are ready for hard use, and at 3.1 pounds, this is a legitimate featherweight for an upper of this capability.
This is a complete upper group—receiver, barrel, gas block, handguard, charging handle, and compensator all assembled and ready to drop onto any compatible lower. No guessing, no missing pieces, no hours of fitting and tuning. If you reload, hunt at intermediate ranges, run suppressors, or just want the punch of a real .338 in a modern rifle platform, the Banshee Mk4 gives you the parts and the platform to make it happen.
| Caliber | .338 ARC |
| Platform | Mk4 |
| Barrel Length | 10.5" |
| Barrel Twist | 1:8 |
| Barrel Material | 4140CM, Nitride Finish |
| Barrel Contour | MT |
| Upper Receiver | Mk4 Billet 6061 T6 Aluminum |
| Handguard | EML9, Cerakote Finish |
| Gas System | Compact Action-Direct Impingement |
| Gas Block | Non-Adjustable, 0.750" |
| Muzzle Device | CMMG ZEROED Linear Compensator |
| Muzzle Thread | 5/8 x 24 |
| Charging Handle | Dissent Side Charger |
| Weight | 3.1 lbs |
| Finish | Black Cerakote |
This is a Mk4 platform upper, so it's compatible with any Mk4-pattern lower receiver. Since it's built on standard AR-15 dimensions and geometry, it'll pair with any quality Mk4 lower you choose.
Yes. The .338 ARC is designed to use the same bolt as 6.5 Grendel AR-15s, so if you already have a Grendel build or bolt, you don't need to duplicate that part.
Yes. The .338 ARC is engineered to run reliably both suppressed and unsuppressed without the gas system tuning headaches that come with other large-bore AR rounds. The non-adjustable gas block is tuned to handle both configurations.
The 1:8 twist is slower than typical modern AR barrels, which allows you to use traditional .338 caliber bullet designs if you're a handloader. This gives you more flexibility in bullet selection and load development.
