All four BHI-15 upper receiver assemblies (A3 flat-top upper w/16- or 20-inch barrel and Slick-Side upper w/16- or 20-inch barrel) are drop-in replacements for your current AR-15 type system ...

The upper includes the barrel, handguard, upper receiver ... and pistol grip. The AR-15's split personality allows a single lower assembly that has a standard size lower receiver to be connected ...

The Upper Receiver ... and any standard AR-15 or M4 barrel extension attached to the upper. This allows it to be compatible even with billet receivers with non-standard dimensions that may ...