This complete upper receiver incudes an HBAR profile barrel that is laser marked HBAR. - Includes: - M4E1 Threaded Assembled Upper Receiver - 15 ATLAS S-ONE M-LOK Handguard - 16 5.56 HBAR Barrel - Low Profile Gas Block and Mid-Length Gas Tube - AR15 A2 Birdcage Flash Hider - Product comes assembled - This complete upper does not include BCG or Charging Handle. - M4E1 Threaded Upper Receiver Features: - New enhanced forging that gives the upper receiver a billet look - New picatinny profile that blends seamlessly with our Enhanced Series Handguards - M4 Feedramps - .250 takedown pin holes - Laser engraved T-marks - Includes port door and forward assist installed - ATLAS 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