CMMG Barrel Sub-Assembly – 8.6 Blackout 12.50" 4140CM Black Nitride – 33D430C
Caliber: 8.6 BLK • Length: 12.50" • Material: 4140CM Chrome-Moly Steel • Finish: Black Nitride • Gas System: Pistol • Thread: 5/8x24 • Twist: 1:3 • MPN: 33D430C • UPC: 810148628734
Unlock the full potential of modern big-bore semi-auto builds with the CMMG Barrel Sub-Assembly 8.6 Blackout 12.50" Black Nitride 4140CM Barrel 33D430C (UPC 810148628734). Engineered specifically for the 8.6 BLK cartridge, this 12.5" nitride-treated barrel is purpose-built for compact AR-10/Mk3 platforms where short overall length, heavy subsonic bullets, and suppressor use are front and center. Whether you’re setting up a hard-hitting hunting rig, a suppressed CQB-style build, or a premium big-bore project, this CMMG factory barrel gives you a rock-solid foundation.
Purpose-Built 12.5" Barrel for Compact 8.6 Blackout Builds
The 12.50" length is the sweet spot for maneuverable 8.6 BLK pistols and SBR-style builds:
Short enough to keep the platform compact and fast-handling, ideal for confined spaces, vehicles, and dense cover.
Long enough to take advantage of the 8.6 BLK’s efficient powder burn and heavy bullet performance, especially with subsonic loads.
Designed around a pistol-length gas system, optimized for reliable cycling in short-barreled big-bore configurations.
If you’re building a compact AR-10 pattern gun that still hits like a freight train, this 12.5" sub-assembly is a natural choice.
4140CM Chrome-Moly Steel with Black Nitride Finish
Durability and longevity start with the right materials and finish:
Barrel is constructed from 4140CM chrome-moly steel, a proven alloy known for strength, toughness, and excellent barrel life under hard use.
Finished in salt bath nitride (SBN), providing superior corrosion resistance, wear resistance, and lubricity compared to traditional bluing or phosphate.
Sleek matte black appearance complements modern receivers and handguards, giving your build a clean, professional look.
This isn’t just a pretty barrel—it’s a workhorse designed to stand up to real-world environmental abuse and high round counts.
Aggressive 1:3 Twist – Designed for Heavy Subsonic Bullets
The defining feature of 8.6 BLK is its very fast twist rate, and CMMG builds this barrel accordingly:
1:3" twist (one turn in 3 inches) is purpose-built for heavy 8.6 BLK projectiles, including long, subsonic bullets where stabilization is crucial.
Optimized to get the most out of suppressed subsonic loads, delivering consistent accuracy and reliable performance.
Still capable of handling supersonic loads, giving you flexibility to tune your build for both quiet shooting and maximum energy on target.
If your goal is to stretch the 8.6 Blackout’s capabilities with heavy, slow, and extremely effective bullets, this twist rate is exactly what you want.
5/8x24 Threaded Muzzle – Suppressor & Muzzle Device Ready
CMMG sets this barrel up to be suppressor-friendly right out of the box:
Standard 5/8x24 muzzle threads for easy installation of 8.6 BLK-compatible suppressors, brakes, or flash hiders.
Ideal for building a quiet, subsonic-focused rig, where a quality suppressor and the 8.6 cartridge shine together.
Threading is machined to industry standards, making it compatible with a broad range of .30-cal and 8.6-specific muzzle devices.
This is a barrel designed from the outset with suppressed performance and modularity in mind.
Mk3 / DPMS Gen 1 High-Pattern LR-308 Compatibility
The CMMG 8.6 BLK 12.5" barrel sub-assembly integrates seamlessly with common AR-10 pattern platforms:
Designed for CMMG Mk3 and DPMS Gen 1 high-pattern LR-308 upper receivers, making it a straightforward choice for many AR-10 builders.
Accepts standard 0.750" diameter gas blocks, opening up a wide range of adjustable and fixed gas block options.
Sub-assembly configuration simplifies pairing with compatible upper components without guesswork on basic fitment.
If you’re starting with a Mk3 or DPMS Gen 1 pattern upper, this barrel is built to drop into that ecosystem. (Always verify fitment with your specific receiver before purchase.)
Compact, Big-Bore Performance for a Variety of Roles
This 12.5" 8.6 Blackout barrel sub-assembly is a strong foundation for several build types:
Hunting rigs: Ideal for medium and large game where heavy bullets, short barrels, and potential suppressed use combine for powerful, ethical performance.
Suppressed tactical/defensive builds: A compact barrel that leverages 8.6 BLK’s heavy subsonic capability for serious close- to mid-range punch.
Range and experimental builds: Perfect for shooters who want to explore the cutting edge of big-bore AR technology beyond traditional .308 and 300 BLK.
In each role, the CMMG sub-assembly gives you factory-engineered quality, not a mystery-spec blank.
Key Specifications – CMMG 33D430C 8.6 Blackout 12.50" Barrel Sub-Assembly
From CMMG and major dealers:
Manufacturer: CMMG
Model: Barrel Sub-Assembly
Platform: Mk3 / AR-10 style (DPMS Gen 1 high-pattern LR-308 compatible)
Caliber: 8.6 Blackout (8.6 BLK)
Length: 12.50"
Material: 4140CM chrome-moly steel
Finish: Black Nitride (Salt Bath Nitride / SBN)
Twist Rate: 1:3"
Gas System: Pistol-length gas port
Muzzle Thread: 5/8x24
Gas Block Diameter: 0.750"
Weight: Approx. 1.7–1.85 lbs (varies slightly by source)
MPN: 33D430C
UPC: 810148628734
Always follow all applicable federal, state, and local laws when configuring 8.6 BLK pistols, SBRs, and suppressed firearms, including all relevant NFA regulations.
SEO-Focused Summary
The CMMG Barrel Sub-Assembly 8.6 Blackout 12.50" Black Nitride 4140CM Barrel 33D430C (UPC 810148628734) is a premium 12.5-inch 8.6 BLK AR-10/Mk3 barrel built from durable 4140CM chrome-moly steel with a corrosion-resistant black nitride finish. Featuring a fast 1:3 twist, pistol-length gas system, 5/8x24 threaded muzzle, and 0.750" gas block compatibility, this 8.6 Blackout barrel is optimized for heavy subsonic loads, suppressed setups, and compact AR-10 builds using CMMG Mk3 or DPMS Gen 1 high-pattern LR-308 upper receivers. For shooters seeking a high-quality barrel to anchor a powerful, compact 8.6 BLK rifle or pistol project, the CMMG 33D430C 12.50" 8.6 Blackout barrel sub-assembly delivers the strength, accuracy, and modern big-bore performance they’re looking for.
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