CMMG Bolt Carrier Group BCG AR15 6.5 Grendel/6mm ARC Black. 5 Grendel or Hornady'S New 6mm Arc. Will not work with our Mkw Platform. Is designed for Standard Ar variants. Specifications for CMMG Bolt Carrier Group (BCG) AR15 6.5 Grendel/6mm ARC: Manufacturer: CMMG Color: Black Finish: Phosphate Fabric/Material: Steel Carrier Material: 8620 Steel Bolt Material: 9310 Steel Caliber: 6mm ARC Gun Make: AR Platform Gun Model: AR-15 Condition: New Package Contents: CMMG Bolt Carrier Group (BCG) AR15 6.5 Grendel/6mm ARC What firearm models does the manufacturer say CMMG Bolt Carrier Group (BCG) AR15 6.5 Grendel/6mm ARC is compatible with? The manufacturer says that CMMG Bolt Carrier Group (BCG) AR15 6.5 Grendel/6mm ARC is compatible with AR-15CMMG 64BA44F: Bolt Carrier Group BCG AR15 6.5 Grendel/6mm ARC Black