CM15 338 ARC Upper Receiver – 16″ AR-15 Upper
The CM15 338 ARC Upper Receiver is Chattahoochee Munitions’ 16-inch upper assembly for the 338 ARC cartridge and AR-15 platform. Built around a lightweight CM billet receiver, 16-inch 1:8 twist CrMV barrel, 15-inch M-LOK handguard, and adjustable gas system, this configuration provides a complete foundation for a customer-built 338 ARC system.
Each 338 ARC Upper Receiver can be configured through the product options. Customers can select the Cerakote finish, B5 rail-cover color, muzzle device, and whether to include the CM15 Low-Mass Bolt Carrier Group and CM15 Warhammer Ambidextrous Charging Handle.
Lightweight CM Billet Upper Receiver
The CM15 uses a lightweight upper receiver CNC machined from 6061 billet aluminum. Machined reliefs are incorporated throughout the receiver to remove unnecessary material, including a milled channel through the Picatinny rail. This receiver configuration is specific to the CM15 upper assemblies and differs from the receiver architecture used on CM15 complete firearms.
- CM lightweight billet upper receiver
- 6061 aluminum construction
- Machined weight-reduction reliefs throughout the receiver
- Milled channel through the Picatinny rail
- Customer-selectable Cerakote finish
16″ 338 ARC Barrel with 1:8 Twist
At the center of the 338 ARC Upper Receiver is a 16-inch CrMV barrel with a 1:8 twist. The barrel uses CM’s DRP profile, a nitride finish, pistol-length gas system, .875-inch gas journal, and 5/8×24 threaded muzzle.
The 16-inch configuration is the longest option in the current CM15 338 ARC upper family. It provides a conventional 16-inch barrel configuration for customers who do not need the compact dimensions of the shorter CM15 10-inch and 8.5-inch uppers.
- 16″ barrel length
- CrMV steel
- DRP profile
- Nitride finish
- 1:8 twist
- Pistol-length gas system
- .875″ gas journal
- 5/8×24 threaded muzzle
Superlative Arms Adjustable Gas System
The CM15 338 ARC Upper Receiver uses a Superlative Arms adjustable gas block paired with a CM Melonite-treated pistol-length gas tube. The adjustable gas system provides a tuning point within the operating system rather than relying on a fixed gas configuration.
- Superlative Arms adjustable gas block
- .875″ gas journal
- Pistol-length gas system
- CM Melonite gas tube
CM 15″ M-LOK Handguard
Surrounding the barrel is a CM 15-inch handguard manufactured from 6061 aluminum. The handguard provides M-LOK mounting capability, a full-length Picatinny top rail, and integrated QD sling sockets at the 3 and 9 o’clock positions.
- CM 6061 aluminum construction
- 15″ handguard length
- M-LOK mounting system
- Full-length Picatinny top rail
- QD sling sockets at 3 and 9 o’clock
- Customer-selectable Cerakote finish
- Customer-selectable B5 rail-cover color
Optional CM15 Low-Mass Bolt Carrier Group
Customers can order the 338 ARC Upper Receiver with or without the CM15 Low-Mass Bolt Carrier Group. This gives customers who already have compatible components the ability to purchase the upper without duplicating the BCG.
When selected, the CM15 Low-Mass Bolt Carrier Group uses a 9310 hardened steel bolt with the requisite 6.5 Grendel Type II / .449″ bolt face for the 338 ARC system.
- 9310 hardened steel bolt
- 6.5 Grendel Type II / .449″ bolt face
- 17-4 stainless-steel firing pin
- 8620 carrier and key
- MPI tested
- Hardened S7 steel extractor
Optional CM15 Ambidextrous Charging Handle
The CM15 upper can also be configured with the CM15 Warhammer Ambidextrous Charging Handle in collaboration with Breek Arms. Customers who already have a compatible charging handle can order the upper without this option.
Selectable Muzzle Device
The 16-inch barrel features a 5/8×24 threaded muzzle. Customers can select from the compatible muzzle configurations available on the product page, including a thread protector or available suppressor-host muzzle devices.
This allows the 338 ARC Upper Receiver to be configured around a customer’s intended suppressor mounting system rather than requiring the replacement of a fixed muzzle device after purchase. Available muzzle-device options and any applicable price differences are shown with the product selections.
Configure Your 338 ARC Upper Receiver
Rather than dividing the CM15 upper family into separate product pages based on finish or accessories, each barrel-length product is configurable. Customers can select the combination appropriate for their build directly from the product page.
- Cerakote finish: Customer-selectable color
- B5 rail covers: Customer-selectable color
- CM15 Low-Mass BCG: With or without
- CM15 Warhammer Ambidextrous Charging Handle: With or without
- Muzzle configuration: Available suppressor-host muzzle device or thread protector
A Purpose-Built 338 ARC Upper
The CM15 338 ARC Upper Receiver is configured as a system rather than simply placing a 338 ARC barrel into a generic upper assembly. The barrel, adjustable gas system, lightweight receiver, handguard, and optional bolt carrier group are selected around the requirements of the cartridge and AR-15 platform.
One of the defining characteristics of 338 ARC is its ability to place a .338-caliber cartridge within the AR-15 platform envelope. The CM15 upper gives customers who already have a suitable lower receiver a direct path into the CM 338 ARC platform without requiring the purchase of a complete firearm.
Why Choose the 16″ CM15 Configuration?
The 16-inch 338 ARC Upper Receiver is intended for customers who prefer a conventional-length AR-15 configuration. Compared with CM’s shorter 10-inch and 8.5-inch uppers, the 16-inch barrel prioritizes barrel length over minimum overall dimensions.
Barrel length can also influence muzzle velocity, with the actual difference depending on the ammunition and load being used. Chattahoochee Munitions therefore offers multiple CM15 barrel lengths so customers can select the configuration that best fits their intended system rather than treating one barrel length as universally preferable.
CM15 16″ 338 ARC Upper Receiver Specifications
- Cartridge: 338 ARC
- Platform: AR-15 / CM15
- Product: Configurable upper assembly
- Upper Receiver: CM lightweight 6061 billet aluminum
- Receiver Features: Machined weight-reduction reliefs and milled Picatinny rail channel
- Finish: Customer-selectable Cerakote color
- Barrel Length: 16″
- Barrel Material: CrMV
- Barrel Profile: DRP
- Barrel Finish: Nitride
- Twist Rate: 1:8
- Gas System: Pistol length
- Gas Journal: .875″
- Gas Block: Superlative Arms adjustable
- Gas Tube: CM Melonite
- Muzzle Thread: 5/8×24
- Handguard: CM 15″ 6061 M-LOK
- Handguard Features: Full Picatinny top rail and QD sockets at 3 and 9 o’clock
- B5 Rail Covers: Customer-selectable color
- BCG: Optional CM15 Low-Mass Bolt Carrier Group
- BCG Bolt: 9310 hardened steel
- Bolt Face: 6.5 Grendel Type II / .449″
- Firing Pin: 17-4 stainless steel
- Carrier and Key: 8620 steel
- Extractor: Hardened S7 steel
- BCG Testing: MPI
- Charging Handle: Optional CM15 Warhammer Ambidextrous Charging Handle in collaboration with Breek Arms
- Muzzle Configuration: Customer-selectable compatible suppressor-host muzzle device or thread protector
Explore Containment Zone 338
Visit Containment Zone 338 to explore CM15 complete firearms, CM15 upper assemblies, CM7S bolt-action systems, barreled actions, magazines, and technical information about 338 ARC.
338 ARC Upper Receiver FAQ
What is included with the CM15 338 ARC Upper Receiver?
The base upper includes the CM lightweight billet receiver, 16-inch barrel, 15-inch handguard, adjustable gas system, gas tube, and selected muzzle configuration. The CM15 Low-Mass Bolt Carrier Group and CM15 Warhammer Ambidextrous Charging Handle are selectable options.
Can I choose the color of the upper?
Yes. Cerakote finish and B5 rail-cover color are customer-selectable options. Available selections are shown on the product page.
Do I have to purchase the BCG and charging handle?
No. The CM15 Low-Mass Bolt Carrier Group and CM15 Warhammer Ambidextrous Charging Handle can be added individually through the product configuration.
Can I select a muzzle device?
Yes. The 5/8×24 threaded barrel can be configured with an available compatible suppressor-host muzzle device or a thread protector.
What twist rate does the 16-inch CM15 338 ARC Upper Receiver use?
The 16-inch CrMV barrel uses a 1:8 twist.
What material is the CM15 upper receiver?
The lightweight CM upper receiver is CNC machined from 6061 billet aluminum and incorporates machined reliefs to reduce unnecessary material.
Does the upper have adjustable gas?
Yes. The CM15 uses a Superlative Arms adjustable gas block with a CM Melonite-treated pistol-length gas tube.
What bolt is supplied when the optional CM15 BCG is selected?
The CM15 Low-Mass BCG uses a 9310 hardened steel bolt with the requisite 6.5 Grendel Type II / .449″ bolt face. The assembly also uses an 8620 carrier and key, 17-4 stainless-steel firing pin, and hardened S7 steel extractor.
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