CMMG Resolute MK4 300 Blackout 16.10in Upper Receiver Armor Black M-LOK Free-Float Handguard for AR-Platform No BCG or Charging Handle. Specifications for CMMG Resolute MK4 300 Blackout 16.10in Upper Receiver: Manufacturer: CMMG Caliber: .300 AAC Blackout Barrel Length: 16.1 in 16 - 16.99 in Finish: Armor Black Color: Armor Black Gun Make: AR Platform Gun Model: AR-15 Additional Features: M-LOK Free-Float Condition: New Magazine Included: No Package Contents: CMMG Resolute MK4 300 Blackout 16.10in Upper Receiver What firearm models does the manufacturer say CMMG Resolute MK4 300 Blackout 16.10in Upper Receiver is compatible with? The manufacturer says that CMMG Resolute MK4 300 Blackout 16.10in Upper Receiver is compatible with AR-15CMMG 30BC40AAB Resolute MK4 300 Blackout 16.10'' Armor Black M-LOK Free-Float