Patent ID: 8230634

Claim:
An upper receiver comprising: a first piece; a backbone, where the backbone is operatively attached to the first piece, where the backbone has a first indexing surface and a second indexing surface, where the backbone has an aperture; a second piece, where the second piece has a first mating surface and a second mating surface; a fastener; a barrel nut having an outer surface, a barrel nut coupling a smooth breech end of a barrel to a front end of the first piece; and an insert, where the insert fits into the aperture, where the insert is configured to receive the fastener, where the second piece is configured to be secured to the first piece by insertion of the fastener through a portion of the second piece and into the insert, where the first indexing surface is configured to contact the first mating surface when the second piece is secured to the first piece, where the second indexing surface is configured to contact the second mating surface when the second piece is secured to the first piece.