Chattahoochee Munitions manufactures this 338 ARC subsonic SBR, a complete factory 10.5-inch CM15 AR15 offered as a pistol with an SBPDW brace or as an SBR with a B5 Systems Bravo stock, with receivers and handguard finished in FDE Metallic Cerakote. It is chambered in 338 ARC with a 10.5-inch 416R stainless barrel and a 1:5 twist, an adjustable gas block and adjustable buffer for subsonic and supersonic ammunition, and a TriggerTech Duty trigger.
338 ARC puts a heavy .338-caliber bullet below the speed of sound in an AR15-size cartridge, and the CM15 is manufactured as a complete 338 ARC system from the factory: barrel, Type II bolt and magazine. See every configuration in Containment Zone 338, and read 338 ARC subsonic.
Why a 338 ARC Subsonic SBR
A 338 ARC subsonic SBR is what the cartridge was designed for: a 307 gr bullet below the speed of sound, an enclosed suppressor and a short barrel. The 10.5-inch CM15 sits near the point where 338 ARC powder use is largely complete in Chattahoochee Munitions testing.
The 1:5 twist spins the subsonic bullet 60 percent faster than 1:8, and the adjustable gas block and buffer let the CM15 cycle subsonic ammunition reliably through a suppressor.
Pistol or SBR Configuration
This 338 ARC subsonic SBR can be ordered as a pistol with an SBPDW telescoping brace and receiver extension, or as an SBR with a six-position receiver extension and a B5 Systems Bravo stock. Length of pull runs 10.25 to 12.75 inches. The SBR configuration is subject to National Firearms Act requirements; see NFA Firearms.
CM15 Receivers and Bolt Carrier Group
The upper and lower are CNC-machined from 7075-T6 billet aluminum with ambidextrous controls. The CM15 low mass bolt carrier group uses a Type II spec 9310 steel bolt with the 6.5 Grendel Type II (.449-inch) bolt face, high-pressure tested and magnetic-particle inspected, with a nitride-coated bolt, carrier and gas key. The CM ambidextrous charging handle is made from 7075 aluminum in collaboration with Breek Arms.
Barrel, Gas and Buffer
The 10.5-inch barrel is 416R stainless steel with a 1:5 twist, finished in E100 Blackout Cerakote, with a shouldered crown and 5/8×24 muzzle threads. The 1:5 twist spins the long 307 gr subsonic bullet 60 percent faster than the 1:8 SAAMI figure, for stability from a short barrel. The pistol-length gas system uses a .750-inch gas journal and a Superlative Arms adjustable gas block, and an Odin Works adjustable buffer completes the tuning, so the CM15 can be set for subsonic or supersonic ammunition, suppressed or not. Read 338 ARC twist rate and 338 ARC barrel length.
Trigger, Handguard and Furniture
The TriggerTech AR15 Duty trigger breaks at 3.5 lb and comes single-stage straight, single-stage curved or two-stage straight. The CM15 LWS 9.5-inch M-LOK handguard is 6061 aluminum with a full-length Picatinny top rail. Furniture is from B5 Systems. The muzzle ships with an optional muzzle brake selection or a thread protector.
Ammunition and Magazine
The 338 ARC subsonic SBR fires SAAMI 338 ARC factory ammunition, including the 307 gr Sub-X subsonic, which Hornady rates at 1,050 fps and 752 ft-lb from a 16-inch barrel, and 170 to 215 gr supersonic loads. Chattahoochee Munitions does not load 338 ARC ammunition. See 338 ARC ballistics.
It ships with one 10-round 338 ARC AR15 magazine in 410 stainless steel, tested by Chattahoochee Munitions with 338 ARC. Standard 5.56 magazines do not feed the wider ARC case. Spares are available as the 338 ARC AR15 magazine.
Suppressing the CM15
With subsonic ammunition, Chattahoochee Munitions recommends an enclosed suppressor rated for .338 caliber or larger. With supersonic ammunition, a flow-through suppressor is recommended to limit back pressure. Use the adjustable gas block to tune for the suppressor you choose. Read the 338 ARC suppressor guide.
FDE Metallic Cerakote Finish
The receivers and handguard are finished in FDE Metallic Cerakote and the barrel in E100 Blackout Cerakote. Mechanical specifications match the Black Tungsten Cerakote and Cobalt Kinetics Green Cerakote models. Other lengths: 8.5-inch CM15 338 ARC, 16-inch CM15 338 ARC. For a bolt action, see the 12.5-inch CM7S 338 ARC and 338 ARC bolt action vs semi auto.
338 ARC Subsonic SBR Specifications
- Manufacturer: Chattahoochee Munitions
- Platform: CM15 AR15, gas operated semi-automatic
- Chambering: 338 ARC
- Configuration: Selectable pistol or SBR
- Barrel: 10.5-inch 416R stainless steel
- Twist rate: 1:5
- Barrel finish: E100 Blackout Cerakote
- Muzzle: 5/8×24 threads, shouldered crown; optional muzzle brake selection or a thread protector
- Gas system: Pistol length, .750-inch gas journal, melonite-treated gas tube
- Gas block: Superlative Arms adjustable
- Buffer: Odin Works AR15 Lite adjustable
- Receivers: CNC-machined 7075-T6 billet aluminum, ambidextrous controls, FDE Metallic Cerakote
- Bolt carrier group: CM15 low mass, Type II spec 9310 steel bolt, 6.5 Grendel Type II (.449-inch) bolt face, nitride coated, HPT and MPI
- Charging handle: CM ambidextrous, 7075 aluminum, made in collaboration with Breek Arms
- Trigger: TriggerTech AR15 Duty, 3.5 lb, single-stage straight, single-stage curved or two-stage straight
- Handguard: CM15 LWS 9.5-inch M-LOK, 6061 aluminum, full-length Picatinny top rail, FDE Metallic Cerakote
- Furniture: B5 Systems
- Pistol rear: SBPDW telescoping brace
- SBR rear: Six-position receiver extension, B5 Systems Bravo stock
- Magazine: One 10-round 338 ARC AR15 magazine, 410 stainless steel, included
- Overall length: 26.54-29.04 inches
- Length of pull: 10.25-12.75 inches
- Weight: 6 lb 10 oz with an unloaded magazine and no accessories; the listing weight is for shipping
338 ARC Subsonic SBR FAQ
Who makes a 338 ARC Subsonic SBR?
Chattahoochee Munitions manufactures this 10.5-inch CM15 338 ARC subsonic SBR, offered as a pistol or SBR, with a 416R 1:5 barrel, adjustable gas and buffer, and a TriggerTech Duty trigger. The CM15 338 ARC is also offered in 8.5, 10.5 and 16 inches, and as the CM7S bolt action.
Does it cycle subsonic 338 ARC?
Yes. The Superlative Arms adjustable gas block and Odin Works adjustable buffer let you tune the CM15 for subsonic or supersonic ammunition, suppressed or not.
Is an SBR configuration available?
Yes. Choose the pistol with an SBPDW brace or the SBR with a B5 Systems Bravo stock. The SBR is subject to National Firearms Act requirements.
What twist rate does it use?
A 1:5 twist in a 10.5-inch 416R stainless barrel.
What bolt does a 338 ARC AR15 need?
A bolt with the 6.5 Grendel Type II bolt face. The CM15 uses a Type II spec 9310 steel bolt in a low mass carrier.
What magazine is included?
One 10-round 338 ARC AR15 magazine in 410 stainless steel. Standard 5.56 magazines do not feed 338 ARC.
What trigger does the CM15 use?
The TriggerTech AR15 Duty at 3.5 lb, in single-stage straight, single-stage curved or two-stage straight.
What suppressor should I use on it?
An enclosed suppressor with subsonic ammunition; a flow-through suppressor with supersonic ammunition. Either must be rated for .338 caliber or larger. The barrel has 5/8×24 threads.
How much does the 10.5-inch CM15 338 ARC weigh?
6 lb 10 oz with an unloaded magazine and no accessories. Any heavier listing weight is the shipping weight.
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