This complete upper assembly makes it easy to convert your 5.56mm AR to 300 AAC BLACKOUT (7.62x35mm).The complete upper comes with the New Knights Armament URX 3.1 Rail that has a 4150 steel barrel features a black nitride finish (including bore and chamber), it has the NEWER 1:7" twist for super- or sub-sonic use. It comes ready for silencer use, threaded 5/8-24 and comes with the 51T Blackout Flash Hider. The bolt carrier group is the NEWER Ni-B Bolt Carrier (Detailed info below).THIS UPPER DOES COME WITH THE KAC URX 3.1 RAIL (SAME RAIL AS IN PICTURE)Detailed Info on Bolt:
The carrier and cam pin are Ni-B. The bolt is conventional.Nickel Boron (Ni-B) UCT EXO coating has a very high hardness and lower friction than either Chrome or Nickel Teflon. There is a base layer of high-phospherous Electroless Nickel which ensures the extreme corrosion protection absent from other Nickel Boron carriers that use a single, thinner layer.Base material is highly polished before coating to ensure the smoothest surface finish.Carrier and cam pin dimensions are custom machined to account for the thicker coatings rather than the more common process of simply coating a conventional carrier with a thin layer.Carpenter 158® phosphated shot-peened bolt to ensure precise dimensions with no concerns for hydrogen embrittlement in the critical lug area.Special green o-ring tested to not bind even at -40 degrees F.Extractor spring made from premium ultra-strong wire - low fatigue design ensures the longest possible life.Extractor pin made from 300 ksi S2 tool steel - not the much lower strength S7 more commonly used.Properly-staked carrier-key with Permatex® gasket-seal compound ensures no gas leakage.
