Here is one of the best .308 rifle upper assemblies you can buy. The Aero Precision AR 308 Upper includes an M4 length gas block, 18" rifle length stainless steel barrel, and an Gen 2 enhanced handguard. The upper itself is a one-piece, free-float design crafted to be one of the strongest, lightweight, and long-lasting assemblies on the market. And the handguard platform is precision machined from 6061-T6 aluminum, and the top Picatinny rail is scalloped to help you mount even more accessories. The upper also features M4 feedramps and a port door, while the takedown pin holes are .2795. This upper receiver is an M5E1 version, which means it is compatible with both receiver extensions. The upper also has a .750 gas block journal, a rifle length gas system, and a forward assist and port door drilled into the barrel. That means you can use standard AR .308 components with this build. For a one-piece, free-floating upper receiver that is built to last and perform to the highest standards, install the Aero Precision AR M5E1 Upper Assembly. Specifications for Aero Precision M5E1 18in .308 Winchester Complete Upper Receiver with Flash Hider: Manufacturer: Aero Precision Caliber: .308 Winchester Barrel Length: 18 in Gas System Length: Rifle Length Barrel Twist Rate: 1-10 Threads per Inch: 5/8x24 Muzzle Device: A2 Flash Hider Gun Model: M5 Condition: New Gun Rail: Picatinny Gun Type: Rifle Gun Make: Aero Precision Included Accessories: None Magazine Included: No Country of Origin: USA Features of Aero Precision M5E1 18in .308 Winchester Complete Upper Receiver with Flash Hider M5E1 Upper Features: Forged from 7075 T6 aluminum Precision machined to our specs M4 feedramps Laser engraved T-marks (Anodized only) .2795 takedown pin holes Accepts standard AR .308 components Comes with forward assist and port door installed Handguard mounting platform is forged into the receiver Gen 2 Enhanced Handguard Features: Added quick disconnect sling socket at the 3, 6 and 9 o'clock positions Milled additional surfaces along flats to aid with gripping and add visual appeal New profile of the Picatinny Top Rail 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 18" .308 4150 CMV Barrel Barrel, Rifle Length Features: .308 Winchester 18" Barrel, 1/10 twist, 4150 CMV, gas port drilled .750 gas block journal Rifle length gas system M4 Feed Ramp Extension HP and MPI tested Standard .308 A2 flash hider Package Contents: Aero Precision M5E1 18in .308 Winchester Complete Upper Receiver with Flash Hider Includes: M5E1 Enhanced Assembled Upper Receiver 15&quot Enhanced M-LOK Handguard 18&quot .308 4150 CMV Barrel Rifle Length Low Profile Gas Block and Rifle Length Gas Tube .308 A2 Birdcage Flash Hider Which weapon models is Aero Precision M5E1 18in .308 Winchester Complete Upper Receiver with Flash Hider compatible with? Aero Precision M5E1 18in .308 Winchester Complete Upper Receiver with Flash Hider is compatible with M5