Fixedcmmg Stock Kit For Mk3 308

The CMMG Stock Kit for Mk3 .308 is a complete buttstock assembly solution for builders putting together a .308 rifle lower receiver. This kit contains everything you need to finish out the rear end of your build—the A1 receiver extension, buffer assembly, action spring, and A1-length buttstock. If you're assembling a .308 rifle from a stripped lower and already have (or are sourcing separately) your lower parts kit, this stock kit handles the business end of the assembly, letting you focus on getting the controls and trigger group installed first.

CMMG designed this kit around the Mk3 platform, so parts are engineered to work together without the guesswork of mixing and matching components from different manufacturers. The A1 receiver extension and matching buffer assembly are straightforward, mil-spec-adjacent pieces that have proven themselves in thousands of builds. The action spring is sized for .308 rifle-length operation, and the A1 buttstock provides a traditional, no-frills cheek weld and mounting system.

This is a builder-focused kit—not a complete lower, and not a drop-in replacement for an existing setup. You'll need a stripped or partially assembled lower receiver and a separate lower parts kit to complete the job. If you already have a lower in progress or on the way, this stock assembly gets you across the finish line without having to source components piecemeal.

What's Included

• A1 Receiver Extension (.308)
• .308 Rifle Buffer Assembly
• .308 Rifle Action Spring
• A1 Rifle-Length Buttstock Assembly

Specifications

Frequently Asked Questions

What do I need to complete my .308 lower receiver with this kit?

This kit includes the receiver extension, buffer, spring, and buttstock. You'll still need a complete lower parts kit (trigger group, controls, etc.) to finish your lower receiver.

Is this kit compatible with other .308 platforms?

This kit is designed for CMMG's Mk3 .308 platform. Compatibility with other .308 rifles is not confirmed by the available information.

Does this include a complete lower receiver?

No. This is a stock assembly kit only. You will need a stripped or partially completed lower receiver to use these components.