CM15 338 ARC Semi Auto SBR – 8.5″ FDE Metallic
The CM15 338 ARC Semi Auto SBR packages the 338 ARC cartridge into an exceptionally compact AR-15-pattern platform. Built around an 8.5-inch 416R stainless-steel barrel with a fast 1:5 twist, this CM15 combines billet 7075-T6 receivers, adjustable gas and buffer systems, a purpose-built bolt carrier group, and a TriggerTech AR15 Duty trigger.
This configuration features FDE Metallic Cerakote with Coyote B5 Systems furniture and a compact 7.25-inch CM15 handguard. The primary SBR configuration uses a six-position adjustable receiver extension and B5 Systems Bravo stock. A pistol configuration using an SBPDW telescoping brace and receiver-extension assembly is also available.
Optics and suppressors shown in product photography are for illustration only and are not included unless specifically identified as part of the selected configuration.
CM15 Billet Upper and Lower Receivers
The 338 ARC Semi Auto SBR is built around the CM15 billet receiver set. Both receivers are CNC machined from 7075-T6 aluminum and incorporate ambidextrous controls and a widely flared magazine well.
- AR-15-pattern receiver architecture
- CNC machined from 7075-T6 billet aluminum
- Pictogram-style Fire/Safe markings on both sides
- Lightened fire-control-group faces and magazine well
- Integral trigger guard
- Machined, widely flared magazine well
- Ambidextrous safety
- Ambidextrous magazine release
- Ambidextrous bolt release
- CM15 pivot and takedown pins
- FDE Metallic Cerakote
TriggerTech AR15 Duty Trigger
The CM15 uses the TriggerTech AR15 Duty trigger. Customers can select from three trigger configurations:
- Single-stage straight bow
- Single-stage curved bow
- Two-stage straight bow
These options provide a choice between single-stage and two-stage operation along with straight- and curved-bow configurations.
CM15 Bolt Carrier Group
The CM15 338 ARC Semi Auto SBR uses a bolt carrier group built around a 9310 steel bolt. The bolt incorporates the requisite 6.5 Grendel Type II / .449″ bolt face for the CM15 338 ARC system.
- 9310 steel bolt
- 6.5 Grendel Type II / .449″ bolt face
- High Pressure Tested (HPT) bolt
- Magnetic Particle Inspected (MPI) bolt
- Nitride-coated bolt
- Nitride-coated carrier
- Nitride-coated gas key
- Hardened gas key
- Grade 8 hardened gas-key fasteners
- Staked gas key
- Tool-steel extractor
CM Ambidextrous Charging Handle
The CM15 is equipped with the CM Ambidextrous Charging Handle in collaboration with Breek Arms. Manufactured from 7075 aluminum, the charging handle provides ambidextrous operation from either side of the firearm.
8.5″ 338 ARC Barrel – 1:5 Twist
At the center of the 338 ARC Semi Auto SBR is an 8.5-inch 416R stainless-steel barrel with a 1:5 twist. Chattahoochee Munitions uses the faster twist in its short 338 ARC configurations based on our experience with heavy .338-caliber projectiles and compact, subsonic-capable systems.
- 8.5″ barrel length
- 416R stainless steel
- E100 Blackout Cerakote
- 1:5 twist rate
- Shouldered crown
- 5/8×24 muzzle threads
- .750″ gas journal
- Pistol-length gas system
Adjustable Gas and Buffer System
The 338 ARC Semi Auto SBR incorporates adjustment at both the gas and buffer systems. A Superlative Arms .750 adjustable gas block provides gas adjustment at the barrel, while the ODIN Works AR15 Lite Adjustable Buffer provides an additional tuning point at the receiver extension.
This gives the compact CM15 adjustment at both ends of the operating system rather than relying on a single fixed gas-and-buffer combination.
- Superlative Arms .750 adjustable gas block
- Melonite-treated pistol-length gas tube
- ODIN Works AR15 Lite Adjustable Buffer
- Adjustable buffer weight
CM15 7.25″ M-LOK Handguard
The 8.5-inch CM15 uses a compact 7.25-inch LWS low-profile handguard finished in FDE Metallic Cerakote. Its shortened profile complements the compact barrel while retaining M-LOK mounting surfaces and a continuous Picatinny top rail.
- 6061 aluminum construction
- 7.25″ length
- Dual-taper attachment system
- Steel barrel nut
- QD sling attachment points at 3 and 9 o’clock
- M-LOK mounting surfaces on sides and bottom
- Full-length Picatinny top rail
- FDE Metallic Cerakote
338 ARC Semi Auto SBR Configuration
The primary configuration of this 338 ARC Semi Auto SBR uses a six-position adjustable receiver extension with a B5 Systems Bravo stock. Combined with the 8.5-inch barrel and 7.25-inch handguard, the configuration emphasizes compact overall dimensions while retaining a conventional stocked AR-15 layout.
A pistol configuration is also available using an SBPDW telescoping brace and receiver-extension assembly. This allows customers to select the configuration that best fits their intended CM15 build.
Short-barreled-rifle configurations are subject to applicable federal, state, and local requirements and transfer through an appropriately licensed dealer.
338 ARC Muzzle Device Options
The 8.5-inch barrel uses 5/8×24 muzzle threads for compatible .338-caliber muzzle devices. Available configurations may include mounting solutions from Q, Dead Air, SilencerCo, Rugged, and other compatible systems. Contact Chattahoochee Munitions regarding specific muzzle-device selections or applicable price differences.
10-Round 338 ARC AR-15 Magazine
The CM15 includes a 10-round DURAMAG SS AR-15-pattern magazine vetted by Chattahoochee Munitions for 338 ARC. The magazine uses 410 stainless-steel construction and is selected as part of the complete CM15 system. For optimal feeding and reliable operation, Chattahoochee Munitions recommends loading the magazine with no more than eight rounds.
Additional magazines are available through the CM 338 ARC AR15 Magazine product page.
Why Choose an 8.5″ 338 ARC Semi Auto SBR?
The 8.5-inch 338 ARC Semi Auto SBR emphasizes compactness while retaining the semi-automatic AR-15 platform and .338-caliber projectile capability of 338 ARC. It is the shortest barrel length in the current CM15 338 ARC family.
In Chattahoochee Munitions testing of the 338 ARC loads we have evaluated, powder utilization occurs largely around the 12-inch barrel-length range. The 8.5-inch configuration therefore represents a deliberate trade between ballistic efficiency and overall compactness rather than an attempt to maximize velocity.
The fast 1:5 twist also reflects CM’s experience with heavy .338-caliber projectiles. In Chattahoochee Munitions testing, the Hornady 307-grain Sub-X has performed better from our 1:5 twist systems than from the standardized 1:8 twist configuration. This is a CM testing observation rather than a claim that 1:5 is universally preferable for every 338 ARC load.
A Purpose-Built Compact Semi-Automatic Platform
The CM15 integrates the components required for 338 ARC into the AR-15 platform rather than treating the cartridge as simply a barrel change. The requisite 6.5 Grendel Type II / .449″ bolt face, CM-vetted magazine, dedicated barrel, adjustable gas block, and adjustable buffer work together as part of the complete system.
The 338 ARC Semi Auto SBR provides a compact semi-automatic counterpart to CM’s CM7S bolt-action 338 ARC configurations while maintaining the smaller AR-15 platform envelope.
Customers can compare both platforms through Containment Zone 338.
CM15 338 ARC Semi Auto SBR Specifications
- Cartridge: 338 ARC
- Platform: CM15 / AR-15 pattern
- Operating system: Gas-operated semi-automatic
- Primary configuration: Short-barreled rifle
- Upper/lower: 7075-T6 billet aluminum
- Finish: FDE Metallic Cerakote
- Barrel: 8.5″ 416R stainless steel
- Barrel finish: E100 Blackout Cerakote
- Twist: 1:5
- Muzzle thread: 5/8×24
- Gas journal: .750″
- Gas system: Pistol length
- Gas block: Superlative Arms .750 adjustable
- Buffer: ODIN Works AR15 Lite Adjustable Buffer
- Bolt: 9310 steel, HPT/MPI
- Bolt face: 6.5 Grendel Type II / .449″
- Charging handle: CM Ambidextrous Charging Handle in collaboration with Breek Arms
- Trigger: TriggerTech AR15 Duty
- Trigger options: Single-stage straight bow, single-stage curved bow, or two-stage straight bow
- Handguard: CM15 LWS 7.25″ M-LOK
- SBR configuration: Six-position adjustable receiver extension with B5 Systems Bravo stock
- Optional pistol configuration: SBPDW telescoping brace and receiver-extension assembly
- Magazine: 10-round DURAMAG SS, CM vetted for 338 ARC. For optimal feeding and reliable operation, Chattahoochee Munitions recommends loading the magazine with no more than eight rounds.
- Weight: 5 lb 14 oz with unloaded magazine and no accessories
- Overall length: 24.5375″–27.0375″
- Length of pull: 10.25″–12.750″
Explore Containment Zone 338
Visit Containment Zone 338 to compare CM15 semi-automatic systems, CM7S bolt-action configurations, barreled actions, magazines, and technical information about 338 ARC.
338 ARC Semi Auto SBR FAQ
What is the CM15 338 ARC Semi Auto SBR?
The 338 ARC Semi Auto SBR is Chattahoochee Munitions’ compact gas-operated AR-15-pattern 338 ARC platform. This configuration uses an 8.5-inch 1:5 twist barrel and a B5 Systems Bravo stock.
Is a pistol configuration also available?
Yes. Customers can select an SBPDW telescoping brace and receiver-extension assembly as an alternative to the SBR configuration.
Why does the 8.5-inch CM15 use a 1:5 twist?
Chattahoochee Munitions uses a fast 1:5 twist in its short 338 ARC configurations. In CM testing, the Hornady 307-grain Sub-X has performed better from our 1:5 systems than from the standardized 1:8 configuration.
Why choose the 8.5-inch barrel?
The 8.5-inch configuration prioritizes compact overall dimensions. Based on CM testing of the loads we have evaluated, it trades some ballistic efficiency relative to longer barrels in exchange for a shorter overall firearm.
Does the CM15 have adjustable gas and buffer systems?
Yes. The CM15 combines a Superlative Arms .750 adjustable gas block with an ODIN Works AR15 Lite Adjustable Buffer.
What bolt face does the CM15 338 ARC use?
The CM15 uses a 9310 steel bolt incorporating the requisite 6.5 Grendel Type II / .449″ bolt face. The bolt is High Pressure Tested and Magnetic Particle Inspected.
What trigger does the CM15 use?
The CM15 uses a TriggerTech AR15 Duty trigger with single-stage straight, single-stage curved, and two-stage straight configurations available.
What magazine is included?
The CM15 includes a 10-round DURAMAG SS AR-15-pattern magazine vetted by Chattahoochee Munitions for 338 ARC. For optimal feeding and reliable operation, Chattahoochee Munitions recommends loading the magazine with no more than eight rounds.
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