CMMG Endeavor MK3 .308 Win 20" Upper Receiver Group - Black

The CMMG Endeavor MK3 .308 Win 20" upper receiver group delivers a working balance between long-range reach and practical handling—ideal for hunters and shooters who refuse to choose between precision and maneuverability. Built on the LR-308/DPMS Gen 1 High-Pattern platform, this Mk3 upper uses direct impingement to run reliably in the field or at the range. The 20-inch 416 stainless steel barrel with a 1:10 twist rate stabilizes mid-weight and heavier .308 rounds, making it a solid pick for both big-game hunting and mid-range tactical work.

What sets this upper apart is the care taken in assembly. It arrives with the bolt carrier group already installed, along with a curated collection of quality parts: a CMMG ZEROED ambi charging handle for left or right-hand operation, a polymer dust cover, and a matched ZEROED muzzle brake (5/8×24 threaded) that helps manage recoil without adding unnecessary length. The billet 7075-T6 aluminum upper and M-LOK compatible hand guard give you a solid foundation for mounting optics, lights, or other accessories.

The MT-profile barrel sits under a 0.750" non-adjustable gas block tuned for rifle-length gas systems, keeping things simple and reliable. At just over 6 pounds and 30.2 inches in overall length, the upper handles well without sacrificing the velocity and energy you expect from a full .308 platform. The Cerakote finish provides durable corrosion protection for years in demanding conditions.

Key Features

• Complete upper receiver assembly—bolt carrier group and hand-selected components included
• Direct impingement operating system for reliable, field-proven performance
• CMMG ZEROED ambi charging handle for ambidextrous operation
• CMMG ZEROED muzzle brake reduces recoil and provides shooter control
• M-LOK hand guard simplifies accessory mounting
• Billet 7075-T6 aluminum upper receiver for strength and durability
• Cerakote finish resists corrosion and wear
• 1:10 twist rate handles a wide range of .308 ammunition

Specifications

Frequently Asked Questions

What platform does this upper receiver fit?

The CMMG Endeavor MK3 upper is built on the Mk3 platform, which follows the LR-308/DPMS Gen 1 High-Pattern design. It is compatible with Mk3 lower receivers.

Is this upper ready to shoot out of the box?

The upper arrives fully assembled with the bolt carrier group installed and includes a muzzle brake, charging handle, and dust cover. You will need to pair it with a compatible Mk3 lower receiver and add a stock, grip, and trigger assembly to complete a functional rifle.

What is the muzzle brake threaded for?

The included CMMG ZEROED muzzle brake is threaded for 5/8×24, which is the standard thread pitch for .308 Winchester rifles. The barrel itself is also threaded to this specification.

Is the charging handle truly ambidextrous?

Yes, the CMMG ZEROED ambi charging handle that ships with this upper works from either side of the receiver, so both left-handed and right-handed shooters can operate it comfortably.