300 Blackout SD SBR or Pistol – CM15 10.5″
The Chattahoochee Munitions CM15 300 Blackout SD is a suppressor-under-handguard firearm manufactured around CM’s preferred 10.5-inch barrel length, 1:5 twist and adjustable operating system. Its extended 13.5-inch handguard surrounds the rear portion of a compatible suppressor, producing an integrated profile while retaining a removable suppressor and serviceable firearm configuration.
This product is available as either a short-barreled rifle or pistol. Chattahoochee Munitions prefers the SBR configuration because its adjustable stock provides consistent shoulder contact while retaining the compact barrel and suppressor relationship that defines the SD system.
The suppressor is not integral to the barrel. The term SD identifies the physical configuration in which a compatible suppressor extends beneath the handguard. A suppressor is sold separately unless it is expressly included through a selected product option.
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.
What Defines the 300 Blackout SD Configuration?
The 300 Blackout SD differs from an ordinary suppressor-ready firearm because the suppressor does not begin entirely beyond the handguard. The 13.5-inch handguard extends four inches forward of the barrel shoulder, allowing part of a compatible suppressor to sit inside the handguard.
This arrangement creates a continuous forward profile, provides additional handguard length and protects the rear portion of the suppressor. The muzzle device, suppressor mount, suppressor diameter and suppressor length must all be compatible with the available internal space.
The handguard has a 1.8-inch internal diameter and accommodates compatible suppressors measuring up to 1.75 inches in outside diameter. The specialized accessory locking nuts positioned near the suppressor section accommodate suppressors up to 1.7 inches in outside diameter.
Suppressor Length and Diameter Requirements
The barrel shoulder sits approximately four inches behind the end of the handguard. A suppressor measuring at least 4.5 inches long is recommended so that a usable portion projects beyond the handguard.
- Handguard overall length: 13.5 inches
- Handguard base length: 9.5 inches
- Barrel shoulder to handguard end: Approximately 4 inches
- Handguard internal diameter: 1.8 inches
- Maximum suppressor diameter: 1.75 inches
- Maximum suppressor diameter around specialized accessory nuts: 1.7 inches
- Recommended minimum suppressor length: 4.5 inches
Suppressor dimensions alone do not guarantee compatibility. The selected mounting system, muzzle device, locking mechanism and required tool access must also fit the available space. Compatibility should be confirmed before finalizing the muzzle-device and suppressor configuration.
SD ZRO 13.5″ M-LOK Handguard
The CM15 300 Blackout SD uses an SLR Rifleworks SD ZRO M-LOK handguard with a 9.5-inch base section and 13.5-inch overall length. Chattahoochee Munitions does not use the optional dowel-pin interface, so that feature is intentionally excluded from this product specification.
- 6061-T6 aluminum construction
- 9.5-inch base length
- 13.5-inch overall length
- 1.8-inch internal diameter
- Free-floating design
- Mil-spec hardcoat-anodized base finish
- 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
- Four specialized accessory locking nuts for the suppressor section
- Handguard weight of approximately 13.9 ounces with barrel nut and hardware
The handguard receives the Cerakote color selected for the firearm. Color is a customer option and does not change the mechanical specifications or search intent of the product.
Heat Considerations for a Suppressor Under the Handguard
A suppressor generates heat, and an SD handguard surrounds part of that heated surface. The handguard can become hot during extended or rapid firing. Shooters should allow the system to cool, use appropriate hand protection when necessary and avoid positioning heat-sensitive accessories where suppressor temperature could affect them.
The suppressor should not contact the handguard or accessory hardware. Adequate clearance must remain around the suppressor to account for manufacturing tolerances, mounting alignment and thermal expansion.
10.5-Inch 1:5-Twist 300 Blackout Barrel
The 10.5-inch barrel places the 300 Blackout SD within CM’s preferred barrel-length range for suppressed and subsonic use. Most useful powder consumption occurs within approximately 9 to 10.5 inches, allowing the firearm to remain compact without giving up meaningful performance for its intended application.
The barrel is manufactured from 4150 CMV steel and receives a nitride treatment. Its 1:5 twist provides the rotational stability preferred for long, heavy subsonic bullets traveling 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
The CM15 uses pistol-length gas on the 10.5-inch barrel. This places the gas port where sufficient pressure remains available to operate the action with subsonic ammunition, particularly when an enclosed suppressor is installed.
The Superlative Arms .750-inch adjustable gas block regulates the amount of 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 unnecessary buffer mass before correcting excessive gas treats the 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.
Enclosed Suppressor Preferred for Subsonic Use
An enclosed suppressor is generally the preferred choice for a 300 Blackout SD intended primarily for subsonic operation. Its backpressure helps operate the action when subsonic ammunition produces comparatively limited gas pressure.
A flow-through suppressor reduces backpressure and is 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 affect cycling even when both loads are subsonic. Final gas adjustment should be performed with the suppressor, ammunition and magazine that will normally be used with the firearm.
For additional information about barrel length, twist rate and load selection, read the 300 Blackout subsonic guide. Purpose-specific ammunition is available from Black Butterfly Ammunition.
CM15 Billet Receiver Set
The upper and lower receivers 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
Customer-Selected Cerakote and Furniture
The single 300 Blackout SD product page includes three coordinated finish packages:
- Cobalt Kinetics Green: Cobalt Kinetics Green Cerakote with Coyote furniture
- FDE Metallic: FDE Metallic Cerakote with Coyote furniture
- Black Tungsten: Black Tungsten Cerakote with black furniture
The selected finish applies to the appropriate receiver, handguard and receiver-extension components. Product photography may show one representative color configuration.
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 grip coordinated with the selected color package
SBR and Pistol Configurations
CM-Preferred SBR Configuration
CM prefers the SBR configuration because an adjustable stock provides consistent shoulder contact while retaining the compact 10.5-inch barrel and suppressor-under-handguard arrangement.
- Six-position adjustable receiver extension
- B5 Systems Bravo stock coordinated with the selected furniture color
- ODIN Works adjustable AR-15 buffer
- Transfer through an appropriate FFL/SOT under applicable NFA requirements
Pistol Configuration
The pistol option uses the same barrel, handguard, upper receiver and adjustable operating system with a pistol-appropriate rear assembly.
- SBPDW brace and receiver-extension assembly
- Cerakote applied to appropriate 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
- 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 Suppressor Interface
The barrel is threaded 5/8×24 and can be configured with a compatible muzzle device or suppressor-mounting interface selected from the available product options. The mount must fit beneath the handguard and provide the access required to install and remove the suppressor safely.
Compatibility must be confirmed for the complete system—not merely the suppressor tube diameter. Certain muzzle-device or mounting selections may affect the final price.
CM-Vetted ETS Magazine
The firearm includes one CM-vetted ETS 30-round magazine. Chattahoochee Munitions treats magazine selection as part of the 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 SD 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 starting point. Final adjustment may still be appropriate when the customer installs a suppressor or changes to ammunition with a substantially different pressure profile.
Complete Specifications
- Manufacturer: Chattahoochee Munitions
- Model: CM15 SD
- 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 SD ZRO M-LOK
- Handguard length: 13.5 inches overall
- Handguard internal diameter: 1.8 inches
- Maximum suppressor diameter: 1.75 inches
- Recommended minimum suppressor length: 4.5 inches
- Magazine: One CM-vetted ETS 30-round magazine
- Finish options: Cobalt Kinetics Green, FDE Metallic or Black Tungsten
- Overall length: 29.5–32.0 inches
Note: Final dimensions and weight can vary according to classification, stock or brace position, muzzle device, suppressor and selected options. Measurements shown elsewhere in the product interface may represent packaged shipping dimensions.
Optics, suppressors and accessories shown in product photography are not included unless expressly identified 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
What does SD mean on this firearm?
SD identifies the suppressor-under-handguard configuration. A compatible removable suppressor extends approximately four inches beneath the handguard. The designation does not mean that the suppressor is permanently integrated into the barrel.
Is a suppressor included?
A suppressor is sold separately unless it is expressly included through a selected product option. Confirm the suppressor diameter, length, mounting interface and required installation clearance before use.
What suppressor diameter fits beneath the handguard?
The handguard accepts compatible suppressors up to 1.75 inches in outside diameter. Suppressors positioned beneath the specialized forward accessory nuts should not exceed 1.7 inches in outside diameter.
Why is a suppressor at least 4.5 inches long recommended?
The handguard extends approximately four inches beyond the barrel shoulder. A suppressor measuring at least 4.5 inches provides some projection beyond the handguard for access and clearance.
Why does CM prefer the SBR configuration?
The SBR combines the compact 10.5-inch barrel and SD handguard with a conventional adjustable stock. This provides consistent shoulder contact while preserving the intended suppressor-under-handguard arrangement.
Can this firearm use subsonic and supersonic ammunition?
Yes, but different loads and suppressors can change operating pressure. The adjustable gas block and adjustable buffer allow the system to be refined for the chosen ammunition and suppressor.
A Purpose-Designed 300 Blackout SD System
The CM15 300 Blackout SD combines CM’s preferred 10.5-inch 1:5-twist barrel with pistol-length gas, adjustable gas control, an adjustable buffer and a 13.5-inch suppressor-compatible handguard. The complete firearm is manufactured, test-fired and verified by Chattahoochee Munitions, with customer-selected classification and color options.
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