This complete upper includes Aero Precision's new ATLAS R-ONE Handguard! The R-ONE handguards are designed with size and weight in mind, while still providing plenty of real-estate to accommodate any attachment needs the end user may have. Aero Precision's proprietary ATLAS attachment system is a durable and dependable mounting platform, maintaining a slim profile while still providing the strength and stability customers have grown to love from Aero Precision handguards. This complete upper does not include a BCG or Charging Handle.Includes: M4E1 Threaded Assembled Upper Receiver ATLAS R-ONE Handguard 14.5" 5.56 Mid-Length CMV Barrel Low Profile Gas Block and Mid Length Gas TubeProduct comes assembledThe muzzle brake that comes with the complete upper receiver is NOT pinned, nor welded, to this barrel. Per the National Firearms Act, the muzzle breake MUST be pinned and welded to achieve the necessary 16" as defined by the ATF for a rifle build.M4E1 Threaded Upper Receiver Features: New enhanced forging that gives the upper receiver a "billet look" New picatinny profile that blends seamlessly with Aero Precision's Enhanced Series Handguards M4 Feedramps .250 takedown pin holes Laser engraved T-marks Includes port door and forward assist installedATLAS R-ONE Handguard Features: Full top picatinny rail for optional attachments Quick disconnect sling socket at the 3, 6 and 9 o'clock positions Compatible with low profile gas blocks 1.3" Inside diameter 1.5" Outside diameter Compatible with mil-spec AR15 upper receivers and barrels14.5" 5.56 Mid-Length Barrel Features: Chamber: 5.56 Length: 14.5" Twist: 1 in 7 Threading: 1/2"x28 Material: Chrome Moly Vanadium Finish: QPQ corrosion resistant finish both inside and out Gas Block: .750 Gas Port: .0785 Gas SystemSpecifications: Caliber/Gauge 5.56x45 Action Semi Automatic Barrel Length 14.5" Barrel Twist 1:7 Barrel Finish QPQ Corrosion Resistant Firearm Fit AR-15 Threaded Barrel Yes Condition NewSegth: Mid Weight: 26oz M4 Barrel Extension HP and MPI Tested