• Caliber: 300 Blackout
  • Finish: Armor Black Cerakote
  • Upper Receiver: CMMG Mk4 Upper Receiver - 6061-T6 Aluminum
  • Handguard: 15-Inch CMMG EML15 Handguard
  • M4 Feed Ramps: Yes
  • Muzzle Device: CMMG A2 Flash Hider
  • Barrel: 16.1" 1:7 Salt Bath Nitrided 4140 Chrome Moly Steel
  • Muzzle Thread Pattern: 5/8"-24
  • Gas Block: CMMG.750" Low-Profile Gas Block
  • Gas Tube: Carbine-Length Gas Tube
  • Bolt Carrier Group: Not Included
  • Charging Handle: Not Included
  • HP and MPI Tested

*This upper assembly does not come with Bolt Carrier Group and Charging Handle


  • Weight: ~3.2 lbs.
  • Length: ~24.56"


  • AR-15 lower receiver


  • 1x CMMG Resolute 300BLK 16.1" MK4 Upper Assembly


300 AAC Blackout, commonly referred to as .300 Blackout, is a popular caliber designed for the AR platform. Its popularity stems from its superior performance with shorter barrels and its versatility as a caliber.

Build Your Perfect AR

Here we have the CMMG Resolute MK4 Upper Assembly, perfect for anyone looking to build an AR chambered in the popular 300 Blackout cartridge. This upper comes in a rifle configuration with a 16.1-inch barrel made from 4140 Chrome Moly Steel and has a Salt Bath Nitride finish. The barrel is threaded with a 5/8"-24 thread pitch and equipped with an A2 flash hider from CMMG.

Precision and Durability Combined

Moving on to the gas assembly, this upper uses a low-profile gas block with a carbine-length gas tube. The 300 Blackout is designed to offer the best ballistic performance from shorter barrels. Therefore, the carbine length gas system allows the rifle to perform smoother.

The gas block and barrel are covered by a 15-Inch CMMG EML15 Handguard. This aluminum handguard has M-LOK slots on both sides and the bottom for mounting accessories and has small sections of Picatinny rail on the front and back of the top for mounting iron sights.

Now let's talk about the receiver. This upper assembly rocks the CMMG Mk4 Upper Receiver. It's made from 6061-T6 aluminum and coated in a sleek Armor Black Cerakote finish. This receiver keeps things light and simple with no forward assist.

Reliable Defense in Your Hands

The CMMG Resolute MK4 Upper Assembly chambered in 300 Blackout is an excellent option for any shooter looking to build a rifle for self-defense. It is designed to be highly reliable, and its parts are HP and MPI tested for quality assurance.

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