CMMG 55DC70A 16.1" Nitrided Barrel Assembly - .223 Remington/5.56 NATO

The CMMG 55DC70A 16.1" nitrided barrel assembly is a complete, drop-in barrel solution built to spec for AR-15 upper builds in .223 Remington/5.56 NATO. Whether you're assembling a new upper receiver or swapping barrels on an existing rifle, this factory-headspaced assembly eliminates guesswork and saves you the hassle of sourcing and timing individual components. It comes ready to install with the M4 barrel extension already properly seated.

Built from 4140 chrome moly steel and finished inside and out with salt bath nitriding, this barrel resists corrosion and wear while delivering the durability serious shooters expect from CMMG. The medium taper profile keeps weight reasonable while maintaining rigidity, and the 1:7 twist rate stabilizes a wide range of .223/5.56 loads—from lightweight 55-grain rounds through heavier modern ammunition. A midlength gas system with a .750" gas journal balances recoil impulse and reliability across different ammunition types.

Threading is 1/2-28, standard for modern AR-15 muzzle devices, so attaching a suppressor, muzzle brake, or flash hider is straightforward. The 16.1" barrel length hits the sweet spot for intermediate-range work, offering velocity gains over shorter carbines while staying handy for tactical applications, hunting, and range work. Since this assembly comes factory-headspaced, you can confidently chamber rounds without secondary headspace verification—critical for safe, reliable function.

Key Features

• Complete barrel assembly with M4 extension properly installed and headspaced
• 4140 chrome moly construction with salt bath nitrided finish for corrosion resistance
• 1:7 twist rate accommodates lightweight through heavy .223/5.56 loads
• 16.1" medium taper profile balances velocity, handling, and recoil
• Midlength gas system with .750" gas journal for reliable function
• 1/2-28 threading for standard AR-15 muzzle devices

Specifications

Frequently Asked Questions

Does this barrel assembly come ready to install on my AR-15 upper?

Yes. The M4 barrel extension is already installed and the barrel is factory-headspaced, so you can mount it directly to your upper receiver without secondary verification.

What ammunition does the 1:7 twist rate handle?

A 1:7 twist is versatile across the .223/5.56 spectrum, stabilizing everything from 55-grain varmint loads to heavier modern match or duty ammunition.

What muzzle devices are compatible with 1/2-28 threading?

Standard AR-15 muzzle brakes, flash hiders, and suppressors threaded 1/2-28 are compatible. This is the industry standard for modern .223/5.56 rifles.

Is this barrel assembly suitable for hunting and long-range shooting?

The 16.1" barrel and 1:7 twist support both applications. The length provides good velocity for hunting and target work, and the twist rate stabilizes a range of load weights for precision shooting.