This Advanced Armament Corp. AR-15 Upper Receiver Assembly in 300 AAC Blackout is a pin-on, ready-to-shoot top end for use with any standard AR-15 lower receiver. The Mil-Spec 4150 chrome moly vanadium steel barrel comes equipped with 1 in 7" twist rifling, M4 feed ramps, a low profile steel gas block, and is finished inside and out with a protective black nitride treatment for superior durability and corrosion resistance. The muzzle is threaded with a 5/8"-24 pitch for easy installation of a silencer, and is topped off with an effective AAC 51T Blackout flash hider.
The upper features a forged M4-Style flat-top receiver onto which a Knight's Armament free floating URX 3.1 Quad Rail System is rigidly attached. The heat-treated, full auto bolt carrier is finished in a slick Nickel Boron coating, and comes equipped with a properly-staked gas key and Carpenter 158 steel bolt assembly.
This 16" 300 Blackout upper utilizes the versatile carbine length gas system, a good choice for this cartridge if various weights and types of ammunition are to be used. Most subsonic and supersonic loads, fired from either a suppressed or unsuppressed gun, are compatible with this configuration. However, some subsonic ammunition may not always cycle reliably under adverse conditions or in a severely fouled firearm without a sound suppressor attached to provide extra backpressure.
