This complete upper receiver incudes an HBAR profile barrel that is laser marked HBAR. – Includes: – M4E1 Assembled Upper Receiver – 15 ATLAS R-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 Upper Features: – Forged from 7075 T6 aluminum – Precision machined to M4E1 specs – M4 feedramps – Matte black hard coat anodized Mil 8625 Type 3 Class 2 – Laser engraved T-marks – Comes assembled with port door and forward assist installed – Accepts standard AR15/M16 components – Handguard mounting platform is forged into the receiver – Works with Aero Precision handguards but also fits most BAR-system handguards – Barrel nut and wrench are included – 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 – 1.3 Inside diameter – 1.5 Outside diameter – Compatible with mil-spec AR15 upper receivers and barrels – MLOK attachment points – 16 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