300 Blackout AR15 Pistol or SBR – CM15 5″
The CM15 300 Blackout AR15 is an exceptionally compact semi-automatic firearm manufactured by Chattahoochee Munitions around a 5-inch, 1:5 twist barrel. Its four-inch handguard, micro-length gas system and adjustable operating components create the shortest conventional-handguard configuration in the CM15 family.
This firearm is available as either a pistol or an SBR. 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 five-inch barrel prioritizes minimum overall length over the greater powder utilization available from the 10- to 10.5-inch barrel range. This is a specialized compact firearm for customers who understand that its principal advantage is portability rather than maximum ballistic performance.
The suppressor, optic and other pictured accessories are not included unless specifically selected or stated in the product options.
Ultra-Compact 300 Blackout AR15
This 300 Blackout AR15 combines a five-inch barrel with a conventional four-inch handguard. The handguard ends behind the muzzle, leaving the muzzle device and suppressor interface accessible. A suppressor remains forward of the handguard rather than extending beneath it.
This configuration is particularly well suited to:
- Compact suppressed subsonic shooting
- Close-range training and range use
- Confined-space handling
- Vehicle transport where legally permitted
- Customers prioritizing minimum firearm length
- Pistol or stocked SBR configurations
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 AR15 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 firearm. Additional information is available from TriggerTech.
Pistol or SBR Configuration
Pistol: SBPDW brace and compatible receiver-extension assembly finished in Black Tungsten Cerakote.
SBR: Six-position receiver extension with a B5 Systems Bravo stock.
CM prefers the SBR 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 applicable 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.
Micro-Length Adjustable Gas System
The 300 Blackout AR15 uses a micro-length gas system because the five-inch barrel is too short to accommodate conventional pistol-length gas. This is a dimensional requirement specific to the five-inch configuration, not a general recommendation for longer 300 Blackout barrels.
- Melonite-treated micro-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 produce substantially different operating conditions.
The gas block addresses the root cause by controlling how much gas enters the operating system. Buffer adjustment provides final refinement after the gas setting is established. The objective is reliable cycling with the lightest practical buffer and the minimum amount of gas required to operate the firearm.
Every CM semi-automatic firearm is test fired and checked for proper operation. 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 detailed information about gas adjustment, buffer adjustment, ejection patterns and single-round testing.
Five-Inch 1:5 Twist Barrel
- 5-inch barrel length
- 4140 GBQ steel
- Nitride finish
- 1:5 twist rate
- Shouldered crown
- 5/8×24 muzzle threads
- .750-inch gas-block journal
- Micro-length gas system
The fast 1:5 twist is essential to the purpose of this short barrel. It provides the rotational stability needed for long, heavy subsonic bullets despite the extremely limited barrel length.
A five-inch barrel does not provide the powder utilization or velocity available from CM’s preferred 10- to 10.5-inch configuration. The defining advantage of this 300 Blackout AR15 is its minimum length rather than maximum ballistic performance.
CM15 LWS Four-Inch Handguard
The CM15 LWS four-inch M-LOK handguard maintains the firearm’s compact profile while covering the micro-length gas system and leaving the muzzle interface accessible.
- 6061 aluminum construction
- Free-floating design
- Dual-taper attachment system
- Steel barrel nut
- QD attachment at the 3 and 9 o’clock positions
- M-LOK mounting surfaces on the sides and bottom
- Full Picatinny top rail
- Black Tungsten Cerakote
Suppressor and Muzzle-Device Options
The 5/8×24 muzzle threads accept compatible 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 selected device.
Any suppressor used with this firearm must be rated by its manufacturer for 300 Blackout and a five-inch barrel. A suppressor’s caliber rating alone does not establish compatibility with an extremely short barrel.
For subsonic ammunition, an enclosed suppressor is generally preferable to a low-backpressure or flow-through design. Subsonic loads often benefit from the additional backpressure supplied by an enclosed suppressor, while a flow-oriented design 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. Even switching between different subsonic loads can affect cycling and ejection behavior.
Subsonic and Supersonic Ammunition
The 300 Blackout AR15 can use both subsonic and supersonic ammunition, but its primary 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 the five-inch barrel limits the cartridge’s velocity potential. Supersonic ammunition also creates a ballistic crack that a suppressor cannot eliminate.
Black Butterfly Ammunition is an appropriate source for purpose-designed 300 Blackout ammunition.
Explore the 300 Blackout subsonic guide for additional 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 magazines are available through the CM15 300 Blackout magazine page.
Product Specifications
- Manufacturer: Chattahoochee Munitions
- Model: CM15 300 Blackout AR15
- Caliber: 300 AAC Blackout / 300 BLK
- Classification: Pistol or SBR
- Barrel: 5-inch 4140 GBQ steel, nitrided
- Twist rate: 1:5
- Gas system: Micro length
- Gas block: Superlative Arms .750-inch adjustable
- Buffer: ODIN Works adjustable AR-15 buffer
- Muzzle thread: 5/8×24
- Handguard: CM15 LWS four-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: 21.0625 to 23.5625 inches
- Weight: 5 pounds 10 ounces 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 AR15 occupies the shortest conventional-handguard position within the CM15 family. Customers wanting the suppressor recessed beneath an extended handguard should consider the five-inch CM15 SD. Customers seeking greater powder utilization should consider a 7.5- or 10.5-inch CM15.
Explore Sector 300 to compare CM15 semi-automatic firearms, CM7S bolt actions, magazines and technical 300 Blackout resources.
Frequently Asked Questions
What is a 300 Blackout AR15?
A 300 Blackout AR15 is an AR-15-pattern firearm chambered for 300 AAC Blackout. This CM15 uses a five-inch barrel and can be configured as either a pistol or an NFA-regulated SBR.
Why does the five-inch barrel use micro-length gas?
The barrel is too short to accommodate a conventional pistol-length gas system. The micro-length system positions the gas port where sufficient operating pressure remains available to cycle the firearm.
Why is a 1:5 twist necessary?
The fast 1:5 twist provides the rotational stability needed for long, heavy subsonic bullets fired through the extremely short barrel.
Is five inches the optimal barrel length for 300 Blackout?
No. CM considers 10 to 10.5 inches optimal for general-purpose 300 Blackout performance. The five-inch barrel is intended for customers who prioritize minimum length over maximum powder utilization and velocity.
Can this firearm be ordered as an SBR?
Yes. Customers can select a six-position receiver extension and B5 Systems Bravo stock. CM prefers the SBR when legally practical because the stock provides greater stability and control.
Can a suppressor be installed?
Yes, but the suppressor must be rated by its manufacturer for 300 Blackout and a five-inch barrel. The four-inch handguard leaves the suppressor and mounting system forward of the handguard.
Is this an SD configuration?
No. This is the conventional-handguard five-inch firearm. The separate CM15 five-inch SD uses an enlarged extended handguard that partially surrounds a compatible suppressor.
Can it fire subsonic and supersonic ammunition?
Yes. Different loads and suppressors can change cycling and ejection behavior, so the adjustable gas block may require retuning 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 21.0625 to 23.5625 inches. The firearm weighs 5 pounds 10 ounces with an unloaded magazine and no accessories. Length of pull adjusts from 10.25 to 12.75 inches.
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