Elevate Your AR-15 Build: The CMMG 16.1" 300 Blackout Barrel Sub-Assembly

Are you an AR-15 enthusiast looking to build a new upper, customize an existing rifle, or simply seeking to upgrade your firearm's performance? For custom builders, serious hobbyists, or anyone aiming for precision and reliability, the CMMG 16.1" 300 Blackout Barrel Sub-Assembly (MPN: 30D120A) is an essential component designed to meet the highest standards. This meticulously crafted barrel sub-assembly offers a robust foundation for a versatile and high-performance AR-15 chambered in the increasingly popular .300 Blackout (300 BLK) caliber.

Why Choose a CMMG Barrel Sub-Assembly for Your AR-15?

Building an AR-15 upper group requires attention to detail, and crucial components like the barrel need to be perfectly aligned and installed. The CMMG Barrel Sub-Assembly simplifies this process by providing a precisely manufactured barrel with the M4 barrel extension already properly installed. This pre-assembly eliminates common headaches associated with torquing the extension and ensuring correct feed ramp alignment, saving builders time, effort, and potential frustrations. It's an ideal solution for anyone asking:

• "What's the best way to ensure proper barrel installation on my AR-15?"
• "How can I streamline the AR-15 upper assembly process?"
• "What components are critical for a reliable AR-15 build?"

CMMG is renowned in the firearms industry for producing high-quality AR platform components. Their dedication to precision engineering and rigorous quality control means that when you choose a CMMG barrel, you're investing in a part that delivers consistent accuracy and exceptional durability. This particular sub-assembly, with its 16.1-inch length, is a prime choice for various applications, from tactical shooting and competitive sports to hunting and personal defense.

Understanding the Power of 300 Blackout

The .300 Blackout (300 BLK) caliber has rapidly gained popularity among AR-15 owners due to its incredible versatility and performance characteristics. Developed to offer improved terminal ballistics over 5.56 NATO in short barrels, and optimized for suppressed fire, 300 BLK offers two primary ammunition types:

• Supersonic Ammunition: These rounds provide excellent ballistics for engagements out to moderate distances, often used for hunting deer or similar-sized game, or for general target practice. Their performance rivals that of the venerable AK-47's 7.62x39mm round, but with the modularity and ergonomics of the AR-15 platform.
• Subsonic Ammunition: Designed to travel below the speed of sound, these heavy rounds shine when paired with a sound suppressor. They offer significantly reduced muzzle report, making them ideal for training, discreet operations, or simply for a more enjoyable shooting experience without disturbing neighbors or wildlife. The CMMG 16.1" barrel with its optimized twist rate (more on that below) is perfectly suited for stabilizing these heavier, slower projectiles.

For shooters considering questions like:

• "What caliber is best for a suppressed AR-15?"
• "Can I hunt with a .300 Blackout AR-15?"
• "What's the difference between supersonic and subsonic 300 BLK?"
• "How does 300 Blackout compare to 5.56 NATO?"

This CMMG barrel provides the ideal foundation to leverage the full potential of the 300 Blackout cartridge, offering flexibility for a wide array of scenarios.

Unpacking the Technical Specifications: What Makes This Barrel Stand Out?

The specific features of the CMMG 16.1" 300 Blackout Barrel Sub-Assembly contribute significantly to its performance, longevity, and ease of integration into your AR-15 build.

Material Excellence: 4140 Chromoly Steel

The barrel is constructed from 4140 Chromoly Steel. This material is a high-strength, low-alloy steel that is widely used in the firearms industry for barrels due to its outstanding properties:

• Durability: 4140 Chromoly offers excellent wear resistance, ensuring the barrel maintains its accuracy and integrity through thousands of rounds.
• Strength: It can withstand the immense pressures generated during firing without deforming, contributing to safety and reliability.
• Heat Resistance: While not as resistant to throat erosion as some other materials, 4140 Chromoly handles typical firing schedules well and is a cost-effective material that still provides superb performance for general use and semi-automatic fire.
• Machinability: This steel is relatively easy to machine, allowing CMMG to achieve precise dimensions and tolerances required for accurate barrels.

For those researching "best barrel materials for AR-15" or "4140 Chromoly vs. 4150 steel," it's important to note that 4140 Chromoly steel barrels are a proven, reliable, and popular choice for their balance of performance and value.

Advanced Protection: Black Nitride Finish

Instead of traditional chrome lining, this CMMG barrel features a Black Nitride finish. This is a surface treatment, not a coating, that chemically hardens the steel's surface. The benefits of Black Nitride are numerous and highly beneficial for a firearm barrel:

• Exceptional Corrosion Resistance: Nitride offers superior protection against rust and environmental damage compared to standard phosphate finishes, crucial for barrels exposed to moisture and gunpowder residue.
• Increased Surface Hardness: The treated surface becomes incredibly hard, significantly improving wear resistance inside and out, leading to extended barrel life and maintained accuracy.
• Enhanced Lubricity: The slick surface reduces friction between the bullet and the bore, which can slightly increase muzzle velocity and reduce fouling, making cleaning easier.
• Thermal Stability: The process is applied at a lower temperature than chrome lining, which means it doesn't negatively affect the barrel's inherent accuracy by stressing the steel.
• Aesthetics: The deep black finish provides a professional and durable appearance that complements any AR-15 build.

When asking "What's the best finish for an AR-15 barrel?" or "Nitride vs. Chrome-Lined barrels," the Black Nitride finish stands out as a modern, high-performance option offering a fantastic balance of durability, accuracy, and ease of maintenance.

Precision Rifling: 1:7" Twist Rate

The barrel features a 1:7" twist rate. The twist rate refers to how many inches of barrel length it takes for the rifling to complete one full rotation. For 300 Blackout, a 1:7" twist rate is considered optimal for stabilizing a wide range of bullet weights, but it particularly excels with heavier, subsonic projectiles (typically 190 grains and above).

• Stabilizing Heavy Subsonics: This faster twist rate imparts more spin on the bullet, ensuring proper gyroscopic stability even with very heavy, long bullets traveling at slower, subsonic velocities. This is critical for accuracy, especially when using a suppressor, as an unstable bullet can "tumble" and potentially strike the suppressor's baffles.
• Versatility: While excelling with heavy bullets, a 1:7" twist can also effectively stabilize most common supersonic 300 BLK ammunition (typically 110-150 grains), making this a highly versatile barrel for diverse ammunition choices.

If you're wondering "What twist rate do I need for 300 Blackout?" or "How does barrel twist affect bullet stability?", the 1:7" twist of this CMMG barrel provides the ideal solution for maximizing the potential of both supersonic and subsonic 300 BLK ammunition.

Carbine-Length Gas System & Threaded Muzzle

This 16.1-inch barrel is designed with a Carbine Length gas port, standard for this length of barrel in the AR-15 platform. This ensures reliable cycling with both suppressed and unsuppressed setups, though fine-tuning with an adjustable gas block is often recommended for optimal suppressed performance.

The muzzle features a 5/8"-24 thread pattern. This is the standard thread pitch for .30 caliber AR-type barrels, allowing for easy attachment of a wide variety of muzzle devices, including:

• Flash Hiders: To reduce muzzle flash signature.
• Muzzle Brakes/Compensators: To mitigate recoil and muzzle rise.
• Sound Suppressors: Crucial for quiet shooting, especially with subsonic 300 BLK ammunition. The standard threading ensures broad compatibility with most major suppressor brands.

This feature is particularly important for those asking "What thread pattern do I need for a 300 Blackout suppressor?" or "How do I attach a muzzle device to my AR-15 barrel?".

Building Your AR-15 Upper with the CMMG Sub-Assembly

The CMMG 30D120A Barrel Sub-Assembly comes ready for integration into your AR-15 upper receiver. Key aspects for assembly include:

• M4 Barrel Extension Pre-installed: As mentioned, this is a significant advantage. The M4 extension includes M4 feed ramps, which are critical for reliable feeding of ammunition, especially in the 300 Blackout caliber which has a different case geometry than 5.56 NATO.
• Gas Block and Gas Tube: You will need to select and install a compatible gas block (typically .750" diameter) and a carbine-length gas tube to complete your gas system.
• Handguard: Choose a free-float or drop-in handguard that is compatible with your upper receiver and gas block.
• Muzzle Device: Select your preferred muzzle device or suppressor to thread onto the 5/8"-24 muzzle.

This barrel sub-assembly is perfect for individuals embarking on a "DIY AR-15 build" or "customizing my AR-15 for 300 Blackout." It provides a high-quality, pre-assembled foundation, simplifying one of the most critical steps in the upper receiver assembly process.

The CMMG Advantage: Quality and Performance You Can Trust

Choosing CMMG for your AR-15 barrel means choosing a company with a proven track record of producing reliable, high-performance firearm components. Their expertise in the AR platform ensures that this barrel sub-assembly isn't just a collection of parts, but a precisely engineered component designed to deliver:

• Consistent Accuracy: From the careful machining of the 4140 Chromoly steel to the precise 1:7" twist rate and durable Black Nitride finish, every aspect of this barrel is designed to maximize accuracy with a wide range of 300 Blackout ammunition.
• Exceptional Durability: The combination of robust materials and advanced finishes translates into a barrel that will withstand extensive use and maintain its performance over time, even in demanding environments.
• Reliable Functionality: The pre-installed M4 barrel extension with proper feed ramps and the optimized carbine-length gas port contribute to the reliable cycling of your AR-15, minimizing malfunctions and ensuring a smooth shooting experience.
• Ease of Assembly: As a sub-assembly, it significantly simplifies the build process, making it more accessible for both experienced builders and those embarking on their first AR-15 project.

In summary, the CMMG 16.1" 300 Blackout Barrel Sub-Assembly (UPC: 815835016238) is more than just a barrel; it's a critical upgrade for anyone seeking to build or enhance a high-performance, versatile, and reliable AR-15 chambered in 300 Blackout. Whether your goal is suppressed shooting, short-range hunting, tactical applications, or simply enjoying the flexibility of the 300 BLK cartridge, this barrel provides the precision, durability, and ease of installation that CMMG is known for.

Product Specifications Overview

Feature	Specification	Benefit
Brand	CMMG	Renowned for quality AR platform components.
Model	Barrel Sub-Assembly	Pre-assembled with M4 extension for easier, precise build.
Caliber	300 Blackout	Optimized for versatile 300 BLK performance, including suppressed fire.
Firearm Fit	AR-15	Seamless integration with standard AR-15 upper receivers.
Length	16.10 inches	Ideal balance of ballistics and maneuverability for 300 BLK.
Material	4140 Chromoly Steel	High strength and durability for long-lasting performance.
Finish	Black Nitride	Superior corrosion resistance, increased hardness, and enhanced lubricity.
Barrel Type	Carbine Length Gas	Designed for reliable cycling with carbine length gas systems.
Twist Rate	1:7"	Optimized for stabilizing a wide range of 300 BLK bullets, especially heavy subsonics.
Thread Pattern	5/8"-24	Standard threading for compatibility with most .30 caliber muzzle devices and suppressors.
Barrel Features	Threaded, M4 Extension	Ready for muzzle devices; pre-installed M4 extension ensures proper feeding and simplifies assembly.
MPN	30D120A	Manufacturer's Part Number for easy identification and ordering.
UPC	815835016238	Universal Product Code for broad retail identification.