RISE Armament's Nickel Boron Bolt Carrier Group is a perfect start to any custom AR-build, or as a solid upgrade to an existing rifle. It features a Nickel boron coating, a columnar-formed compound composed of about 95 percent nickel and 5 percent boron. This formation reduces the contact points between surfaces while simultaneously providing an additional level of hardness to the steel. The result is a natural lubricity and improved durability. When compared to the industry standard chrome coating, the nickel boron coating offers greater resistance to corrosion for a significantly longer service life.