Building an AR-15 from the ground up, or refreshing an existing platform? The CMMG 6-Position Mil-Spec AR-15 Aluminum Buffer Tube Assembly is the backbone of your rifle's stock interface and recoil system. This receiver extension kit delivers the adjustability and reliability you need to dial in length-of-pull for your shooting style, whether you're working with body armor, layering up for cold-weather hunts, or just fine-tuning ergonomics for the range. CMMG's six-position design lets you customize fit across a range of configurations—critical when you're balancing comfort, control, and repeatability.

The aluminum construction keeps weight minimal while maintaining the mil-spec dimensions that work with standard AR-15 furniture and components. This buffer tube assembly is engineered to function reliably with most common carbine-length AR platforms, making it a straightforward drop-in for builds, repairs, or upgrades. If you're completing a lower receiver or swapping out worn rear-end components, this kit simplifies the process by bundling the core pieces you need into one package.

CMMG has built its reputation on no-nonsense AR components that do the job without the noise. This assembly reflects that ethos—solid engineering, proven compatibility, and honest performance. It's the kind of part you grab when you know exactly what you need and want to move forward with confidence.

Key Features

• Six-position adjustable length-of-pull for custom fit and ergonomics
• Mil-spec aluminum construction for durability and weight efficiency
• Carbine-length compatible with standard AR-15 platforms
• Complete assembly kit—all components included to finish your receiver extension

Specifications

Brand	CMMG
Product Type	Buffer Tube Assembly / Receiver Extension Kit
Position Adjustment	6-Position
Material	Aluminum
Specification Standard	Mil-Spec
Compatibility	AR-15 (Carbine-Length)
Color	Black

Frequently Asked Questions

Will this buffer tube fit my AR-15 build?

This CMMG assembly is designed to be compatible with most standard carbine-length AR-15 platforms. It follows mil-spec dimensions, so it will work with standard AR furniture and components.

What's included in this kit?

The CMMG 6-Position Receiver Extension Kit includes the six-position aluminum buffer tube, carbine-style buffer assembly, and action spring—everything needed to complete your receiver extension.

Can I adjust the length-of-pull?

Yes. The six-position design allows you to adjust the overall length-of-pull across multiple positions, so you can customize fit for your body mechanics, gear, or shooting preference.

Is this better than a fixed tube?

Adjustability lets you dial in the exact fit for your application. Whether you're running light gear, body armor, or just prefer a shorter or longer stock position, the six-position option gives you flexibility that a fixed tube doesn't.