A monolithic upper receiver/hand guard is provided for use with a firearm. The monolithic upper receiver/hand guard can include an upper receiver section, a hand guard section, and an interrupted optics rail extending along the top of the upper receiver section and the hand guard section. Cable routing features can be defined in the hand guard section and/or the upper receiver section for helping to control wires and cables extending from or between peripheral devices and accessories, which can be mounted on the monolithic upper receiver/hand guard. The cable routing features can include one or more crossover cable guides disposed in respective channels in the interrupted optics rail. The crossover cable guide can include one or more grooves for receiving a portion of a cable passing from one side of the monolithic upper receiver/hand guard to the other for connecting two peripheral devices, for example.