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Sourcing buffer system parts one at a time is a good way to end up with a drawer full of odds and ends and a lower that still won't cycle. CMMG cut out the guesswork here by packaging every piece you need to complete the back end of an AR-15 lower into a single kit. You get their 6-position mil-spec receiver extension, a carbine buffer, the action spring, a castle nut, and an end plate, all matched to work together right out of the package.
The tube itself is machined from aluminum with a matte black hard coat anodized finish, so it holds up to real range time and repeated stock adjustments. Being mil-spec, it measures right around 1.148 inches at the stock end, which is the diameter the vast majority of aftermarket stocks are built around. That means once this tube is on your lower, you can bolt up nearly any carbine stock or brace without chasing down compatibility charts. The six positions give you room to dial in length of pull for different shooters, layered clothing, or optics setups.
Mil-spec has become the default standard across the AR world, and for good reason. The rolled threads and tighter tolerances give you a solid lockup and the widest possible selection of stocks down the road. The included carbine buffer and action spring are tuned for standard carbine-length gas systems running 5.56 NATO, so you get reliable cycling without having to guess at buffer weights on a typical build.
Keep in mind this kit covers the buffer system only. To finish the lower you'll still need a lower parts kit, a grip, and the stock or brace itself. Installation is straightforward with the castle nut and end plate included, though a castle nut wrench and a little blue thread locker make the job cleaner. For anyone completing a lower or replacing a worn tube, this is a no-nonsense way to get quality CMMG components in one shot.
This is a mil-spec receiver extension, measuring right around 1.148 inches at the stock end. Mil-spec is the standard the majority of aftermarket stocks are designed around, so you'll have the widest selection when picking a stock or brace. If you're unsure what your current tube is, a quick measurement with calipers will tell you, since commercial tubes run closer to 1.17 inches.
No, the stock or brace is not included. The kit covers the buffer system itself, meaning the tube, carbine buffer, action spring, castle nut, and end plate. You just add the mil-spec carbine stock or brace of your choice to finish the back end of the lower.
Beyond this buffer system kit, you'll need a lower parts kit, a pistol grip, and a stock or brace. The lower parts kit handles the trigger group, safety, and other small internals. Once those are in and this receiver extension is torqued down with the castle nut, your lower is functionally complete.
Yes. The included carbine buffer and action spring are matched for standard carbine-length gas systems running 5.56 NATO, so it drops right into a typical build. If you find your rifle runs overgassed, you can always step up to a heavier buffer later, but the standard carbine setup covers most builds well.
| UPC | 815835017389 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | 55CA6C7-RETAIL |
| Color | Black |
| Length | 13.0500 |
| Model | |
| Product Type | Receiver Extension Kit |
| Shipping Weight | 0.625 |
| Style | Extension |
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