Aero Precision APAR700305M48: This complete upper includes Aero Precision\'s new ATLAS S-ONE Handguard! The S-ONE line of handguards are designed with size and weight in mind, providing the perfect addition to your lightweight build. 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 BCG or Charging Handle. Includes: M4E1 Threaded Assembled Upper Receiver 15\" ATLAS S-ONE Handguard 20\" 5.56 Rifle Length CMV Barrel Low Profile Gas Block and Rifle Length Gas Tube Product comes assembled 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 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 Compatible with low profile gas blocks 1.3" Inside diameter 1.5" Outside diameter Compatible with mil-spec AR15 upper receivers and barrels 20\" 5.56 Rifle Length CMV Barrel Features: 5.56 NATO 20\" Rifle Length, 1/7 twist, 4150 CrMoV, QPQ, gas port drilled .750 gas block journal Government Profile Rifle length gas system, .0785 gas port M4 Feed Ramp Extension HP and MPI tested Standard A2 flash hider