With this complete upper receiver, you can finish your new build with confidence that you can handle any situation or that you're over-equipped. Aero Precision built these AR Handguards & Barrels with their ATLAS S-ONE Handguard and 20in 5.56 Rifle length barrel for top-shelf quality. The handguard included with this Aero Precision Complete Upper Receiver w/ ATLAS S-ONE Handguard includes indexing grooves at the 12:00 position for positive grip control during shooting sessions. Also, the top rail on these uppers is cut from the center of the top rail, reducing the weight. There's a quick-disconnect sling socket at the 3:00 and 9 o'clock positions so that you can carry your rifle on your side or use a sling for added mobility. Complete your rifle build with this high quality Aero Precision M4E1 Threaded NATO w/ ATLAS S-ONE Handguard Complete Upper Receiver Package.Specifications: Gun Model: M16, AR-15 Fabric/Material: 4150 CrMoV Cartridge: 5.56x45mm NATO Barrel Profile: Government Gas Block Journal Size-Diameter: .750 in Barrel Twist Rate: 1-7 Handguard Style: Hybrid Rail Gun Rail: M-LOK Muzzle Device: A2 Flash Hider Gun Make: Aero Precision, AR Platform Gas System Type: ProprietaryFeatures: 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 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 Compatible with mil-spec AR15 upper receivers and barrels 4150 CrMoV, QPQ, gas port drilled .0785 gas port M4 Feed Ramp Extension HP and MPI tested Standard A2 flash hiderPackage Contents: 5.56 CMV Barrel (Carbine Length) Low Profile Gas Block Carbine Length Gas Tube