The CMMG Resolute MK4 upper receiver assembly represents CMMG's newest long-range offering chambered in Hornady's innovative 6mm ARC (Advanced Rifle Cartridge) for superior function and accuracy at extended ranges.CMMG Resolute MK4 Complete Upper Assembly6mm ARC caliber for long-range precision16.1" threaded barrel for optimal performanceCerakote Armor Black finish for durabilityPrecise manufacturing and long-term reliabilityCompatible with existing AR15 lower receiversDurable construction for demanding useDesigned to pair seamlessly with your existing AR15 lower this complete upper assembly delivers exceptional accuracy and performance for long-range shooting applications.