The CMMG A1 Receiver Extension (brand part number 55CA9B7) is a rifle-length buffer tube built to the AR-15/M4/M16/LR-308 pattern, designed to accept a fixed rifle-length stock rather than an adjustable carbine stock. CMMG machines the extension from black hard coat anodized aluminum for durability, and it is compatible with both Mk4 (AR-15) and Mk3 (LR-308) lower receivers, covering builders working in either the 5.56 or .308 pattern. It is a direct, mil-spec-pattern part for anyone building or converting a rifle to run a fixed stock instead of a collapsible one.

Key Specifications

• Rifle-length buffer tube, built for fixed rifle-length stocks.
• AR-15/M4/M16/LR-308 pattern.
• Black hard coat anodized aluminum.
• Compatible with Mk4 (AR-15) lower receivers.
• Compatible with Mk3 (LR-308) lower receivers.

Frequently Asked Questions

Does this fit an adjustable carbine stock? No, it is a rifle-length extension designed to accept a fixed rifle-length stock.

What lower receivers is it compatible with? Mk4 (AR-15) and Mk3 (LR-308) lower receivers.

Buy the CMMG A1 Receiver Extension

Convert your build to a fixed rifle-length stock with a direct, mil-spec-pattern extension. Order it from our Lubbock, Texas gun shop for fast, insured shipping, and browse more AR buffer system parts.