Cmmg 12.5'' Bbl Sub-Assy Mc 1-10 5/8-24'' Black Nitride

The CMMG 12.5" barrel sub-assembly is a complete, ready-to-assemble upper component for builders working with .308 Winchester platform rifles. If you're putting together a custom MK3 upper receiver group or need a verified, headspaced barrel solution for a midrange build, this assembly arrives with the barrel extension already installed and properly seated—one less step between you and a functioning upper.

Built on a medium taper contour and fitted with a mid-length gas system, this sub-assembly delivers the kind of balance that works for both accuracy work and practical rifle use across a range of distances. The 1-10 twist rate handles a wide spectrum of .308 Winchester ammunition weights, from lighter target loads to heavier hunting rounds. Threading is 5/8-24, the standard for suppressors and muzzle devices in the .308 world.

The salt bath nitride finish is CMMG's answer to durability: it hardens the steel without adding visible bulk, resists corrosion, and cleans up easily after a range session. You're getting a component that's been verified for headspace, so you can build with confidence rather than spending your build day at a gunsmith.

Key Features

• Pre-installed, verified barrel extension—eliminates a critical assembly step
• Properly headspaced and ready to mate with your upper receiver
• Medium taper contour: balance between rigidity and overall handling weight
• Mid-length gas system suited to 12.5" barrel length
• 1-10 twist accommodates standard .308 Winchester loads across a broad weight range
• 5/8-24 threading for suppressors and muzzle devices
• Salt bath nitride finish for corrosion resistance and easy maintenance

Specifications

Frequently Asked Questions

Can I use this barrel sub-assembly in an AR-10 or .308 platform upper?

This CMMG sub-assembly is designed for .308 Winchester rifles with MK3 upper receiver groups. If you're building or replacing an upper, confirm your upper's platform matches CMMG's MK3 specification before ordering.

Is the barrel extension already installed?

Yes. The barrel extension comes pre-installed and properly seated, so you can proceed directly to upper receiver assembly.

What ammunition weights does the 1-10 twist handle?

A 1-10 twist is stable across the standard range of .308 Winchester loads. You're not locked into one weight range; this twist supports both lighter target ammunition and heavier hunting rounds used in .308 Winchester.

What suppressor or muzzle device will fit the 5/8-24 threading?

The 5/8-24 thread pitch is the industry standard for .308 Winchester suppressors and muzzle devices. You have a wide selection of compatible options from most major manufacturers.