Gorilla Machining is proud to offer our very own Mil-Spec Forward Assist Assembly and Dust Cover Kit for the. Perfect for replacing your existing component or replacing worn or broken parts. AR-15 Upper Receiver Parts Kit includes all the pieces for a standard upper receiver assembly. The kit from Rise Armament includes a dust cover, pin, spring, and c-clip, as well as a forward assist, spring and roll pin. The AR-15 Upper Receiver Parts Kit has everything you need for your upper receiver in a 7 Piece Standard Upper Parts Kit.