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 Product comes assembled This complete upper does not include BCG or Charging Handle.M4E1 Threaded Upper 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 installedATLAS S-ONE Handguard Features: Front and rear picatinny rail Eliminated center of top rail for weight reduction Indexing grooves in 12:00 position for positive grip control Quick disconnect sling socket at the 3, 6 and 9 o'clock positions 1.3" Inside diameter 1.5" Outside diameter Compatible with mil-spec AR15 upper receivers and barrels MLOK attachment points16" 5.56 HBAR Barrel 5.56 Nato 16" Barrel, 1/7 twist, 4150 CrMoV, QPQ, gas port drilled .750 gas block journal Mid-Length Gas System M4 Feed Ramp Extension HP and MPI tested Standard A2 flash hider