- Product Code: 55CA9D7
CMMG Receiver Extension Mk4 - mil-spec 6-position carbine receiver extension (buffer tube) for AR-15/M4 platforms, made of aluminum and finished with matte black hard coat anodizing; it accepts mil-spec type carbine-length stocks and pistol brace solutions, providing a reliable and dimensionally compatible foundation for stock length adjustment.
Precise dimensions and finish provide confidence in installation: mil-spec diameter fits directly with mil-spec dimensioned carbine stocks, and the 6-position adjustment offers flexible length adjustment for different users and equipment setups. The hard coat anodized (typically Type III) surface improves wear resistance, and the matte black finish reduces reflections and simplifies maintenance. The structure is designed to be used with a carbine-length buffer and recoil spring.
Special note: mil-spec body outer diameter supports a wide range of M4-type, mil-spec dimensioned stock options. A standard end plate and castle nut (not included) are used as counterparts, and installation is done on an AR-15 lower receiver with 1-3/16-16 UN threads (approximately 30.2 mm x 16 TPI). It conforms to carbine standard length dimensions, with an overall length of approximately 184 mm (7.25 in). Compatibility with the CMMG Mk4 platform is direct, and the product works with other AR-15/M4-compatible lower receivers as long as the dimensions are mil-spec.
CMMG Receiver Extension Mk4 - Features:
- Type: AR-15/M4 carbine receiver extension (buffer tube), mil-spec
- Adjustment: 6-position length adjustment
- Material: aluminum
- Finish: matte black hard coat anodizing (typically Type III)
- Stock compatibility: mil-spec dimensioned carbine-length buttstocks and pistol brace solutions
- Buffer system compatibility: carbine-length buffer and recoil spring
- Thread: 1-3/16-16 UN (approximately 30.2 mm x 16 TPI)
- Outer diameter: mil-spec 1.148 in (approximately 29.1 mm)
- Overall length: approximately 184 mm (7.25 in)
- Finish: matte black, reflection-reducing
- Manufacturer: CMMG
- Model: Mk4
Summary: This receiver extension is a mil-spec dimensioned, 6-position, hard coat anodized solution for AR-15/M4 systems. It offers reliable compatibility with mil-spec carbine stocks, precise length adjustment, and a durable surface designed for demanding use.
Recommended use: suitable for building and upgrading AR-15/M4 platforms when seeking a mil-spec compatible, adjustable stock solution foundation.
Product text updated on 6.3.2026.
