CM15 300 Blackout 10.5″ 1:5 AR15 SBR or Pistol – Cobalt Kinetics Green

300 Blackout AR15 SBR or Pistol – CM15 10.5″

The Chattahoochee Munitions CM15 is a complete 300 Blackout AR15 SBR manufactured around the barrel length, twist rate and adjustable operating system CM prefers for subsonic and suppressed 300 Blackout use. Customers may order this firearm as a short-barreled rifle or pistol, but Chattahoochee Munitions prefers the SBR configuration as the most complete expression of the system.

The 10.5-inch barrel falls within CM’s optimal 10 to 10.5-inch range for 300 Blackout. Its 1:5 twist provides the rotational stability preferred for long, heavy subsonic bullets. A pistol-length gas system, Superlative Arms adjustable gas block and ODIN Works adjustable buffer allow the firearm to be tuned for the ammunition and suppressor being used.

Every CM semi-automatic firearm is test-fired and verified for proper operation before shipment. Chattahoochee Munitions addresses barrel gas-port sizing, gas-block alignment and baseline operating-system adjustment during manufacturing.

Explore the complete Sector 300 ecosystem for additional CM15 and CM7S firearms, technical resources, magazines and supporting products.

Why CM Prefers the 300 Blackout AR15 SBR

The 300 Blackout AR15 SBR configuration combines the cartridge’s efficient barrel length with the stability and consistent shoulder contact of an adjustable rifle stock. For CM’s preferred subsonic application, a 10 to 10.5-inch barrel provides an effective balance of powder utilization, handling and suppressor compatibility.

Most useful powder consumption occurs within approximately 9 to 10.5 inches. Extending the barrel beyond that range does not provide a meaningful advantage for CM’s intended subsonic use. The 10.5-inch barrel avoids unnecessary length while leaving sufficient space for a conventional pistol-length gas system.

Customers who do not want the additional federal requirements associated with an SBR may select the pistol configuration. The barrel, handguard, gas system and upper-receiver components remain the same. The rear assembly changes according to the firearm classification selected by the customer.

10.5-Inch 1:5-Twist 300 Blackout Barrel

The barrel is manufactured from 4150 CMV steel and receives a nitride treatment. The 1:5 twist is particularly important for stabilizing long, heavy subsonic bullets at relatively low velocity.

• Caliber: 300 AAC Blackout / 300 BLK
• Barrel length: 10.5 inches
• Barrel material: 4150 CMV steel
• Barrel finish: Nitrided
• Twist rate: 1:5
• Crown: Shouldered crown
• Muzzle thread: 5/8×24
• Gas journal: .750 inch
• Gas-system length: Pistol length

Pistol-Length Gas and Adjustable Operation

This 300 Blackout AR15 SBR uses pistol-length gas because the cartridge must retain sufficient operating pressure when firing subsonic ammunition. Moving the gas port farther forward would reduce the pressure available to operate the action and could make reliable subsonic cycling more difficult.

The Superlative Arms .750-inch adjustable gas block regulates the gas entering the operating system. The ODIN Works adjustable buffer provides a secondary tuning control after the appropriate gas setting has been established.

The objective is reliable feeding, extraction, ejection and last-round bolt lock with the lightest practical buffer and the minimum gas required. Adding buffer mass before correcting excessive gas treats a symptom instead of addressing the source of the operating pressure.

Read the 300 Blackout gas-system guide for CM’s complete explanation of gas adjustment, ejection patterns, buffer tuning and suppressor backpressure.

Subsonic and Suppressed Performance

A 10.5-inch 300 Blackout AR15 SBR is particularly well suited to heavy subsonic ammunition and an enclosed suppressor. An enclosed suppressor generates backpressure that helps operate the action when subsonic ammunition produces comparatively limited gas pressure.

Flow-through suppressors reduce backpressure and are generally better suited to supersonic-focused cartridges. Reduced backpressure can work against reliable subsonic cycling. Conversely, supersonic ammunition combined with an enclosed suppressor may generate enough backpressure that the adjustable gas block must be closed substantially.

Changing ammunition can alter cycling even when both loads are subsonic. The gas setting should therefore be established using the ammunition, magazine and suppressor that will normally be used with the firearm.

For more information about barrel length, twist rate and ammunition selection, read the 300 Blackout subsonic guide. Purpose-specific loads are available from Black Butterfly Ammunition.

SLR Rifleworks ZRO 9.5″ M-LOK Handguard

The CM15 uses an SLR Rifleworks ZRO 9.5-inch M-LOK handguard. Its exact 9.5-inch length leaves the muzzle of the 10.5-inch barrel accessible for compatible 5/8×24 muzzle devices and suppressor-mounting systems.

The free-floating handguard includes a continuous Picatinny top rail, M-LOK accessory mounting and two limited-rotation QD sling sockets. Its forward accessory space is well suited to appropriately mounted lights, night-vision equipment and infrared aiming devices.

• 9.5-inch exact length
• 1.35-inch internal diameter
• Free-floating design
• Mil-spec hardcoat-anodized construction
• Hardcoat-anodized 7075 aluminum barrel nut
• No barrel-nut timing or shims required
• Slip-fit locking mounting system
• Two limited-rotation QD sling sockets
• Continuous Picatinny top rail
• M-LOK accessory attachment
• Cobalt Kinetics Green Cerakote exterior finish

CM15 Billet Receiver Set

The upper and lower receivers of this 300 Blackout AR15 SBR are CNC-machined from 7075-T6 billet aluminum. Their close fit contributes to the rigid, substantial feel associated with the CM15 platform.

• Mil-spec component interface dimensions
• CNC-machined 7075-T6 billet aluminum construction
• Ambidextrous pictogram-style Safe and Fire markings
• Lightened fire-control-group faces and magazine well
• Integral trigger guard for additional receiver strength
• Machined rather than broached magazine well
• Wide magazine-well flare
• Lower receiver weight of approximately 8 ounces
• Cobalt Kinetics Green Cerakote finish

Ambidextrous Controls and TriggerTech Duty Trigger

The CM15 lower receiver includes ambidextrous controls and a customer-selectable TriggerTech AR15 Duty trigger. Available options are single-stage curved, single-stage straight and two-stage straight. All three options have a 3.5-pound total pull weight.

• CM ambidextrous safety selector
• CM ambidextrous magazine release
• CM15 ambidextrous bolt release
• CM15 pivot and takedown pins
• TriggerTech AR15 Duty trigger selected by the customer
• B5 Systems Coyote grip

SBR and Pistol Configurations

Preferred SBR Configuration

CM prefers the 300 Blackout AR15 SBR configuration because the adjustable stock provides consistent shoulder contact while preserving the handling benefits of the 10.5-inch barrel.

• Six-position adjustable receiver extension
• B5 Systems Bravo stock
• ODIN Works adjustable AR-15 buffer
• Transfer through an appropriate FFL/SOT under applicable NFA requirements

Pistol Configuration

The pistol option provides the same CM15 upper, barrel, gas system and handguard with a pistol-appropriate rear configuration.

• SBPDW brace and receiver-extension assembly
• Cobalt Kinetics Green Cerakote on applicable extension components
• ODIN Works adjustable AR-15 buffer

The selected configuration determines the firearm’s classification. Customers are responsible for compliance with all applicable federal, state and local requirements.

CM15 Bolt Carrier Group

The CM15 bolt carrier group operates as part of the complete adjustable system rather than as an isolated component.

• 9310 steel bolt
• High-pressure-tested bolt
• Magnetic-particle-inspected bolt
• Nitride-coated bolt
• Nitride-coated carrier
• Nitride-coated gas key
• Gas key hardened to USGI specifications
• Grade 8 hardened gas-key fasteners
• Gas key staked to military specifications
• Tool-steel extractor

Upper Receiver Components

• CM15 ambidextrous charging handle machined from 7075 aluminum
• CM15 dust cover
• Melonite-treated pistol-length gas tube
• Superlative Arms .750-inch adjustable gas block with Melonite finish

Selectable 5/8×24 Muzzle Device

The 10.5-inch barrel is threaded 5/8×24 and can be configured with an appropriate muzzle device or suppressor-mounting interface selected from the available product options. The final device should match the suppressor or unsuppressed configuration the customer intends to use. Certain selections may affect the final price.

Legacy photography may show a muzzle device that is not the current default configuration. The completed firearm is not restricted to the device pictured.

CM-Vetted ETS Magazine

The firearm includes one CM-vetted ETS 30-round magazine. Chattahoochee Munitions treats magazine selection as part of the firearm’s operating system because cartridge presentation and feeding can vary with different 300 Blackout bullet profiles.

Additional magazines are available through the 300 Blackout magazine product page.

Factory-Tested and Verified

Every 300 Blackout AR15 SBR or pistol manufactured by Chattahoochee Munitions is test-fired and checked for proper semi-automatic operation before shipment. Gas-port sizing, gas-block alignment and baseline tuning are addressed during manufacturing instead of being left as unresolved customer troubleshooting.

The factory setting establishes a reliable operational baseline. Final gas adjustment may still be appropriate when the customer changes ammunition or adds a suppressor with a substantially different backpressure profile.

Complete Specifications

• Manufacturer: Chattahoochee Munitions
• Model: CM15
• Caliber: 300 AAC Blackout / 300 BLK
• Available classifications: SBR or pistol
• Barrel: 10.5-inch 4150 CMV, nitrided
• Twist rate: 1:5
• Gas system: Pistol length
• Gas block: Superlative Arms .750-inch adjustable
• Buffer: ODIN Works adjustable AR-15 buffer
• Muzzle thread: 5/8×24
• Trigger: TriggerTech AR15 Duty, 3.5-pound total pull
• Handguard: SLR Rifleworks ZRO 9.5-inch M-LOK
• Magazine: One CM-vetted ETS 30-round magazine
• Finish: Cobalt Kinetics Green Cerakote with Coyote furniture
• Pistol overall length: 26.5375–29.0375 inches
• Pistol length of pull: 10.25–12.75 inches
• Listed weight: 6 pounds, 10 ounces with an unloaded magazine and no accessories

Note: The listed overall length and length of pull apply to the pistol configuration represented by the available technical baseline. The SBR configuration varies with stock position. Weight and dimensions shown elsewhere in the product interface may represent packaged shipping measurements.

Optics and suppressors shown in product photography are for illustration only unless expressly included in the selected product options.

Limited Lifetime Warranty

• Limited to the original purchaser
• Limited regarding functional performance
• Limited regarding the firearm’s original configuration

Frequently Asked Questions

Why does CM prefer the 300 Blackout AR15 SBR?

The SBR combines CM’s preferred 10.5-inch barrel with a conventional adjustable stock. It provides consistent shoulder contact while preserving the compact handling for which short 300 Blackout firearms are selected.

Can this firearm be ordered as a pistol?

Yes. Customers may select the pistol configuration instead of the SBR. The upper, barrel, gas system and handguard remain consistent, while the rear assembly changes according to the selected classification.

Is a 10.5-inch barrel effective with subsonic ammunition?

Yes. Chattahoochee Munitions considers approximately 10 to 10.5 inches optimal for its preferred subsonic use of 300 Blackout. The 1:5 twist provides additional stability for long, heavy subsonic bullets.

Can the firearm use a suppressor?

Yes. The muzzle is threaded 5/8×24 and remains accessible beyond the 9.5-inch handguard. An enclosed suppressor is generally preferable when reliable subsonic operation and maximum sound reduction are the primary objectives.

Does the firearm require adjustment when ammunition changes?

It may. Different subsonic and supersonic loads can produce different operating pressure. The adjustable gas block and adjustable buffer allow the system to be refined for the ammunition and suppressor being used.

A Complete 300 Blackout System

The CM15 Cobalt Kinetics Green 300 Blackout AR15 SBR combines CM’s preferred 10.5-inch barrel length, a 1:5 twist, pistol-length gas, adjustable gas control, an adjustable buffer and a free-floating ZRO handguard. The complete firearm is manufactured, test-fired and verified by Chattahoochee Munitions for compact handling and suppressed subsonic performance.