The core of BHI-15's upper receiver program is a medium-contour Criterion barrel (a division of Kreiger Barrels) made of 4140 steel that's button-rifled and chrome-lined for durability. Featuring ...

The upper includes the barrel, handguard, upper receiver, charging handle and bolt carrier group (BCG). The bottom half, or “lower,” contains all of the components needed to fire an AR-15.