Upgrade the performance of your AR15 build with this Aero Precision AR-15 M4E1 Upper Receiver Assembly. The S-ONE line of handguards are designed with size and weight in mind, providing the perfect addition to your lightweight build. The 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. All other components are standard to the AR15 platform. This upper assembly does not include a BCG or Charging Handle. Includes:M4E1 Threaded Assembled Upper ReceiverATLAS S-ONE Handguard.750 Low Profile Gas Block and Mid Length Gas TubeA2-style Flash Hider FeaturesEnhanced forging that gives the upper receiver a "billet look"Picatinny profile that blends seamlessly with Enhanced Series Handguards.250 takedown pin holesLaser engraved T-marksIncludes port door and forward assist installedFront and rear picatinny railEliminat...