CM15 300 Blackout 7.5″ AR15 SBR or Pistol – Black Tungsten

300 Blackout Semi-Auto SBR or Pistol – CM15 7.5″

The CM15 300 Blackout Semi-Auto SBR is a compact AR-15 firearm manufactured by Chattahoochee Munitions for suppressed shooting, close-range handling and applications where overall length matters. Its 7.5-inch barrel, 6.7-inch handguard and adjustable operating system create a highly maneuverable firearm with the gas control required for dependable 300 Blackout operation.

This CM15 is available as either an SBR or a pistol. Chattahoochee Munitions prefers the stocked SBR configuration when legally practical because the shoulder stock provides greater stability, control and consistency. The pistol remains available for customers whose intended use or ownership requirements favor that classification.

The 7.5-inch barrel intentionally prioritizes compactness over the greater powder utilization available from the 10- to 10.5-inch barrel range. Its 1:5 twist supplies the rotational stability needed for long, heavy subsonic bullets fired through a shortened barrel.

Compact 300 Blackout Semi-Auto SBR

This 300 Blackout Semi-Auto SBR is designed for customers who deliberately prioritize reduced overall length and maneuverability. Its short barrel and handguard make the firearm easier to handle in confined spaces while helping manage the additional length of a suppressor.

The conventional 6.7-inch handguard ends behind the muzzle, leaving the muzzle device and suppressor interface accessible. This differs from the CM15 SD configuration, where part of the suppressor extends beneath an enlarged handguard.

This configuration is particularly well suited to:

• Compact suppressed shooting
• Close-range training and range use
• Confined-space handling
• Property and personal-defense applications
• Vehicle transport where legally permitted
• Customers who prefer the control of a stocked SBR

CM15 Billet Receiver Set

The matched CM15 upper and lower receivers are CNC machined from 7075-T6 billet aluminum. Tight receiver fit, ambidextrous controls and a flared machined magazine well create a rigid and functional foundation for the complete firearm.

• Mil-spec interface dimensions for AR-15 components
• CNC-machined 7075-T6 billet aluminum construction
• Black Tungsten Cerakote
• Ambidextrous pictogram-style Safe and Fire markings
• Lightened fire-control-group faces and magazine well
• Integral trigger guard for additional strength
• Machined, rather than broached, magazine well
• Wide magazine-well flare
• Lower receiver weight of approximately 8 ounces

Ambidextrous Lower Controls

• CM ambidextrous safety selector
• CM ambidextrous magazine release
• CM15 pivot and takedown pins
• CM15 ambidextrous bolt release
• B5 Systems Black grip

TriggerTech Duty Trigger Options

Each 300 Blackout Semi-Auto SBR is offered with a TriggerTech AR-15 Duty trigger. Customers can select from three 3.5-pound configurations:

• Single-stage curved
• Single-stage straight
• Two-stage straight with a 3.5-pound total pull weight

TriggerTech’s design provides a clean, predictable break while maintaining the durability appropriate for a working AR-15. Additional information is available directly from TriggerTech.

SBR or Pistol Configuration

SBR: Six-position receiver extension with a B5 Systems Bravo stock.

Pistol: SBPDW brace and compatible receiver-extension assembly finished in Black Tungsten Cerakote.

CM prefers the SBR configuration when legally practical because its shoulder stock provides more consistent support and control. An SBR is regulated under the National Firearms Act and must be transferred through an appropriately licensed FFL/SOT following the required federal process. Customers remain responsible for compliance with federal, state and local law.

Both configurations use an ODIN Works adjustable AR-15 buffer. Buffer adjustment complements the adjustable gas block and permits final refinement without relying on unnecessarily heavy reciprocating mass.

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

The upper assembly also includes a CM15 ambidextrous charging handle machined from 7075 aluminum, dust cover and forward assist.

Adjustable Pistol-Length Gas System

The 300 Blackout Semi-Auto SBR uses a pistol-length gas system. Pistol gas is necessary for dependable 300 Blackout operation across the cartridge’s broad pressure range, including heavy subsonic ammunition. The 7.5-inch barrel provides sufficient room for pistol gas; CM’s shorter 5-inch configurations require a micro-length gas system.

• Melonite-treated pistol-length gas tube
• Superlative Arms .750-inch adjustable gas block
• ODIN Works adjustable buffer
• Gas system configured and verified during manufacturing

An adjustable gas block is a requisite component on a properly configured semi-automatic 300 Blackout firearm. Subsonic ammunition, supersonic ammunition and suppressors can create substantially different operating conditions.

The gas block addresses the root cause by controlling how much gas enters the operating system. Buffer adjustment can then provide final refinement when necessary. The objective is reliable operation with the lightest practical buffer and no more gas than the firearm requires.

Every CM semi-automatic firearm is test fired and checked for proper operation before shipment. Gas-port sizing, gas-block alignment and baseline system tuning are addressed during manufacturing rather than being left for the customer to diagnose.

Explore the 300 Blackout gas-system and tuning guide for a detailed explanation of gas adjustment, buffer adjustment, ejection patterns and single-round testing.

7.5-Inch 1:5 Twist Barrel

• 7.5-inch barrel length
• 4150 chrome-moly-vanadium steel
• Nitride finish
• 1:5 twist rate
• Shouldered crown
• 5/8×24 muzzle threads
• .750-inch gas-block journal
• Pistol-length gas system

The fast 1:5 twist is especially important in this short barrel. It provides greater rotational stability for long, heavy subsonic bullets than the former 1:7 configuration. This makes the revised barrel substantially better aligned with the suppressed and subsonic purpose of 300 Blackout.

A 7.5-inch barrel does not provide the same powder utilization as CM’s preferred 10- to 10.5-inch configuration. The advantage of this 300 Blackout Semi-Auto SBR is its reduced length, particularly after a suppressor is installed.

SLR Rifleworks ZRO 6.7-Inch Handguard

The firearm uses an SLR Rifleworks ZRO 6.7-inch M-LOK handguard. Its short length provides clearance for the muzzle device and suppressor attachment interface while retaining useful accessory-mounting space.

• 6.7-inch exact length
• 1.35-inch internal diameter
• Free-floating construction
• Mil-spec hardcoat-anodized finish beneath the Cerakote
• Hardcoat-anodized 7075 aluminum barrel nut
• No barrel-nut timing or shims required
• Slip-fit locking attachment system
• Two limited-rotation QD sling sockets
• Continuous Picatinny top rail
• M-LOK accessory-mounting surfaces
• Useful forward mounting space for compatible night-vision and infrared equipment
• Black Tungsten Cerakote

Suppressor and Muzzle-Device Options

The 5/8×24 muzzle threads accept commonly used 300 Blackout muzzle devices and suppressor-mounting systems. Available selections may include direct-thread devices, flash hiders, brakes and suppressor mounts. Pricing may vary according to the device selected.

For subsonic 300 Blackout, an enclosed suppressor is generally preferable to a low-backpressure or flow-through design. Subsonic ammunition often benefits from the additional backpressure supplied by an enclosed suppressor. A flow-oriented suppressor can reduce the operating energy available to cycle the firearm.

Supersonic ammunition used with an enclosed suppressor can generate considerably more backpressure. The adjustable gas block allows incoming gas to be reduced rather than attempting to mask excessive gas with a heavier buffer alone.

Suppressor choice, ammunition and gas settings function as an interconnected system. Changing any one of them can require adjustment. Even switching between different subsonic loads can affect cycling and ejection behavior.

Subsonic and Supersonic Ammunition

The 300 Blackout Semi-Auto SBR can use both subsonic and supersonic ammunition, but its principal purpose is compact suppressed operation with subsonic loads.

Subsonic ammunition provides the cartridge’s defining suppressed capability. Supersonic ammunition produces greater velocity and energy, but it also changes gas-system behavior and creates a ballistic crack that a suppressor cannot eliminate.

Load selection should be based on the intended application, bullet construction and the firearm’s verified operating configuration. Black Butterfly Ammunition is an appropriate source for purpose-designed 300 Blackout ammunition.

Explore the 300 Blackout subsonic guide for more information about barrel length, twist rate, ammunition and suppression.

CM-Vetted 300 Blackout Magazine

Each firearm includes one CM-vetted ETS 30-round magazine. Magazine performance is evaluated as part of the complete firearm system rather than assuming every nominally compatible AR-15 magazine will feed every 300 Blackout load equally well.

Additional vetted magazines are available through the CM15 300 Blackout magazine page.

Product Specifications

• Manufacturer: Chattahoochee Munitions
• Model: CM15 300 Blackout Semi-Auto SBR or pistol
• Caliber: 300 AAC Blackout / 300 BLK
• Classification: SBR or pistol
• Barrel length: 7.5 inches
• Barrel material: 4150 CMV
• Barrel finish: Nitride
• 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
• Handguard: SLR Rifleworks ZRO 6.7-inch M-LOK
• Trigger: TriggerTech Duty with selectable 3.5-pound configuration
• Magazine: One CM-vetted ETS 30-round magazine
• Finish: Black Tungsten with Black furniture
• Overall length: 23.875 to 26.375 inches
• Weight: 6 pounds with an unloaded magazine and no accessories
• Length of pull: 10.25 to 12.75 inches

Note: Weight and dimensions shown on another product tab are for shipping purposes.

Limited Lifetime Warranty

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

Explore Sector 300

This 300 Blackout Semi-Auto SBR occupies a compact conventional-handguard position within the CM15 family. Customers seeking greater powder utilization should consider a 10.5-inch CM15. Customers wanting the suppressor recessed beneath the handguard should consider the dedicated 7.5-inch SD configuration.

Explore Sector 300 to compare CM15 semi-automatic firearms, CM7S bolt actions, uppers, barreled actions, magazines and technical 300 Blackout resources.

Frequently Asked Questions

What is a 300 Blackout Semi-Auto SBR?

A 300 Blackout Semi-Auto SBR is a semi-automatic firearm chambered in 300 Blackout with a shoulder stock and a barrel shorter than 16 inches. This CM15 uses a 7.5-inch barrel and is regulated under the National Firearms Act when configured as an SBR.

Can this CM15 be ordered as a pistol?

Yes. Customers can select a pistol configuration with an SBPDW brace instead of the stocked SBR configuration. CM prefers the SBR when legally practical because the stock provides greater stability and control.

Why does the 7.5-inch barrel use a 1:5 twist?

The 1:5 twist provides increased rotational stability for long, heavy subsonic bullets fired through the short barrel. It is better aligned with the suppressed and subsonic purpose of this firearm than the former 1:7 twist.

Is a 7.5-inch barrel optimal for 300 Blackout?

No. Chattahoochee Munitions considers 10 to 10.5 inches the optimal general-purpose barrel range for 300 Blackout. The 7.5-inch configuration is intended for customers who deliberately prioritize minimum overall length and maneuverability.

Does this firearm use pistol-length gas?

Yes. The 7.5-inch barrel uses a pistol-length gas system. CM’s shorter 5-inch configurations require a micro-length gas system because those barrels are too short to accommodate pistol gas.

Can a suppressor be installed?

Yes. The barrel has 5/8×24 muzzle threads, and the 6.7-inch handguard leaves the muzzle device and suppressor mounting interface accessible. The suppressor remains forward of the conventional handguard.

Is the suppressor recessed beneath the handguard?

No. This is the conventional 7.5-inch configuration. Customers wanting part of the suppressor beneath the handguard should select the dedicated CM15 7.5-inch SD configuration.

Why are both the gas block and buffer adjustable?

The adjustable gas block controls how much gas enters the operating system and addresses the root cause of overgassing or insufficient operating energy. The adjustable buffer permits final refinement after the gas setting has been established.

Can it use subsonic and supersonic ammunition?

Yes. Different loads and suppressors can change system pressure, cycling and ejection behavior, so gas adjustment may be required when the operating configuration changes.

Is every CM15 test fired?

Yes. Every CM semi-automatic firearm is test fired and checked for proper operation. Gas-port sizing, gas-block alignment and baseline tuning are addressed during manufacturing.

What magazine is included?

One CM-vetted ETS 30-round magazine is included. Chattahoochee Munitions evaluates magazine compatibility as part of the complete firearm system.

What are the firearm’s dimensions and weight?

The overall length is 23.875 to 26.375 inches. The firearm weighs 6 pounds with an unloaded magazine and no accessories. Length of pull adjusts from 10.25 to 12.75 inches.