This Complete Upper 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. This assembly does not include BCG or Charging Handle. These products may be selected as add-ons under the FINISH YOUR BUILD tab The muzzle brake that comes with this complete upper receiver is NOT pinned nor welded to this barrel. Per the National Firearms Act, the muzzle brake MUST be pinned and welded to achieve the necessary 16" as defined by the ATF for a rifle build. Specifications for Aero Precision M4E1 10in .300 Barrel Complete Upper with Flash Hider: Manufacturer: Aero Precision Cartridge: .300 AAC Blackout Barrel Length: 10 in Muzzle Device: A2 Flash Hider Condition: New Gun Type: Rifle Gun Make: Aero Precision Magazine Included: No Country of Origin: USA Features of Aero Precision M4E1 10in .300 Barrel Complete Upper with Flash Hider: 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 (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 Barrel nut and wrench are included   GEN 2 ENHANCED HANDGUARD FEATURES: 1pc free float design 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 Gen 2 Feature - Quick disconnect sling socket at the 3, 6 and 9 o'clock positions Gen 2 Feature - Additional milling along flats to aid with gripping and add visual appeal Gen 2 Feature - New profile for the continuous picatinny top rail 10" .300 BLACKOUT BARREL FEATURES: Length: 10" Twist: 1 in 7 Muzzle: 5/8x24 Threaded Material: 4150 Crome Moly Vanadium Finish: QPQ corrosion resistant finish both inside and out Gas Block: .750 Gas Port: .0935 Gas System Length: Pistol Weight: 21oz M4 Barrel Extension HP and MPI Tested Aero Precision M4E1 10in .300 Barrel Complete Upper with Flash Hider M4E1 Enhanced Assembled Upper Receiver Enhanced Handguard of choice 10" .300 Blackout CMV Barrel Low Profile Gas Block and Pistol Length Gas Tube Product comes assembled This assembly does not include BCG or Charging Handle. These products may be selected as add-ons under the FINISH YOUR BUILD tab The muzzle brake that comes with this complete upper receiver is NOT pinned nor welded to this barrel. Per the National Firearms Act, the muzzle brake MUST be pinned and welded to achieve the necessary 16" as defined by the ATF for a rifle build.