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. Specifications for Aero Precision M4E1 Enhanced 14.5in 5.56 M4 Carbine Length Barrel Complete Upper Receiver with Flash Hider: Manufacturer: Aero Precision Caliber: 5.56x45mm NATO Barrel Length: 14.5 in Barrel Twist Rate: 1-7 Muzzle Device: A2 Flash Hider Gun Model: AR-15 Condition: New Handguard Length: 12 in Magazine Included: No Country of Origin: USA Features of Aero Precision M4E1 Enhanced 14.5in 5.56 M4 Carbine Length Barrel Complete Upper Receiver 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 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 1.78in inside diameter fits most muzzle devices and 1.5in suppressors Compatible with low profile gas blocks Gen 2 Feature - Quick disconnect sling socket at the 3 6 and 9 oclock 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 14.5in 5.56 M4 CMV Barrel Carbine Length Features: 5.56 Nato 14.5in Barrel 1/7 twist 4150 CrMoV QPQ gas port drilled .750 gas block journal Carbine length gas system .0785 gas port M4 Feed Ramp Extension HP and MPI tested Standard A2 flash hider Included Accessories: M4E1 Enhanced Assembled Upper Receiver Enhanced Handguard of choice 14.5in 5.56 M4 CMV Barrel Carbine Length Low Profile Gas Block and Carbine Length Gas Tube Product comes assembled This complete upper 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 16in as defined by the ATF for a rifle build. What firearm models does the manufacturer say Aero Precision M4E1 Enhanced 14.5in 5.56 M4 Carbine Length Barrel Complete Upper Receiver with Flash Hider is compatible with? The manufacturer suggests that Aero Precision M4E1 Enhanced 14.5in 5.56 M4 Carbine Length Barrel Complete Upper Receiver with Flash Hider is compatible with AR-15