Aero Precision APAR640231M5: This Complete Upper includes Aero Precision\'s 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 complete upper does not include BCG or Charging Handle. Includes: M4E1 Enhanced Assembled Upper Receiver 12\" Enhanced Gen 2 M-LOK Handguard 14.5\" 5.56 Mid-Length CMV Barrel Low Profile Gas Block and Mid Length Gas Tube Product comes assembled The muzzle brake that comes with this complete upper receiver is NOT pinned nor welded to this barrel. 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 1.78\" 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 14.5\" 5.56 Mid-Length Barrel Features: Chamber: 5.56 Length: 14.5\" Twist: 1 in 7 Threading: 1/2\"x28 Material: Chrome Moly Vanadium Finish: QPQ corrosion resistant finish both inside and out Gas Block: .750 Gas Port: .0785 Gas System Length: Mid Weight: 26oz M4 Barrel Extension HP and MPI Tested