This Upper Receiver Handguard Combo now includes our Gen 2 Enhanced Handguard! Key features include the addition of quick disconnect sling sockets, enhanced milling design for grip and visual appeal and a new profile for the picatinny top rail. Anti-Rotation Tabs. Feed Ramp Extension. Scalloped Rails. Continuous Top Rail. Specifications for Aero Precision M4E1 AR-15 10.5in 5.56 Rifle Barrel Complete Upper Receiver with Flash Hider: Manufacturer: Aero Precision Cartridge: 5.56x45mm NATO Barrel Length: 10.5 in Gas System Length: Rifle Length Barrel Twist Rate: 1-7 Handguard Type: Free-Float Muzzle Device: A2 Flash Hider Gun Model: M16, AR-15 Fabric/Material: 7075 T6 Aluminum Attachment/Mount Type: Picatinny Handguard Length: 9 in Gun Type: Rifle Gun Make: Aero Precision, AR Platform Barrel Material: 4150 Chrome Moly Vanadium Gas Block Journal Size-Length: 0.75 in Bolt Carrier Group Included: No Charging Handle Included: No Features of Aero Precision M4E1 AR-15 5.56 Rifle Barrel Complete Upper Receiver with Flash Hider: 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 (Anodized only); 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; Features of Enhanced Handguard: 1pc free float design; Rail is Machined from 6061-T6 Aluminum; Built in Anti-Rotation tabs; Scalloped rails; Continuous top rail; 1.78" inside diameter fits most muzzle devices and 1.5" suppressors; Compatible with low profile gas blocks; Quick disconnect sling socket at the 3, 6 and 9 o'clock positions; Additional milling along flats to aid with gripping and add visual appeal; New profile for the continuous picatinny top rail Features of 5.56 Rifle Length Barrel: 4150 CrMoV w/ QPQ finish; 1/7 twist; .750 gas block journal; Rifle length gas system; M4 Feed Ramp Extension; HP and MPI tested; Standard A2 flash hider Package Contents: Aero Precision M4E1 AR-15 10.5in 5.56 Rifle Barrel Complete Upper Receiver with Flash Hider Enhanced Handguard 5.56 Rifle Length CMV Barrel Low Profile Gas Block and Rifle Length Gas Tube Barrel Nut Wrench