Cmmg Barrel Sub-Assm 18.0Inch Ht 416Ss 308 Win

The CMMG 18-inch barrel sub-assembly in .308 Winchester gives you a precision-engineered foundation for a custom MK3 upper build. This is a complete barrel assembly—not just a tube—so it arrives pre-installed with the barrel extension and properly headspaced, ready to integrate into your receiver group. Heavy taper profile, 416 stainless steel construction, and a professional bead-blasted finish deliver the durability and accuracy you'd expect from a purpose-built AR platform barrel.

Built on a 1:10 twist rate suited to .308 Winchester, this barrel handles a wide range of factory and handloaded ammunition. The rifle-length gas port and .936-inch gas journal pair with standard AR-10 systems, and the 5/8-24 threading accepts suppressors, muzzle devices, and precision brakes without modification. Eighteen inches hits the balance point many shooters prefer: compact enough for hunting or tactical work, long enough to preserve velocity and maintain sight radius without unnecessary weight.

CMMG's sub-assembly approach removes guesswork from the build. Headspacing and extension fitment are already verified at the factory, so you can focus on the rest of your upper rather than hunting down a gunsmith for critical tolerances. The stainless steel resists corrosion through field use and storage, and the heavy profile soaks up recoil while delivering consistent shot placement from the bench or in the field.

Key Features

• Pre-installed barrel extension with factory headspacing verification
• 416 stainless steel with bead-blasted finish for corrosion resistance
• Heavy taper profile for recoil management and thermal stability
• 1:10 twist optimized for .308 Winchester across factory and handload ranges
• Rifle-length gas system with .936-inch gas journal for standard AR-10 compatibility
• 5/8-24 threading for suppressors and muzzle devices

Specifications

Frequently Asked Questions

Is this barrel assembly compatible with AR-10 upper receivers?

Yes. The barrel extension is pre-installed and the .936-inch gas journal is standard for AR-10 rifle-length systems. It integrates directly into MK3 upper groups and compatible AR-10 platforms.

Do I need to have the headspacing checked before use?

No. CMMG verifies proper headspacing during assembly, so it arrives ready to use once installed in your upper receiver and lower group.

What is included in this sub-assembly?

The barrel sub-assembly includes the 18-inch stainless steel barrel, the pre-installed barrel extension, and the properly headspaced assembly. You will need to source a separate bolt carrier group and other upper components to complete the build.

Can I use a suppressor with this barrel?

Yes. The 5/8-24 muzzle threading accepts standard suppressors and muzzle devices designed for .308 Winchester rifles.