Abstract: A rail system for a firearm includes an elongate body that is fastenable to the firearm to at least partially enclose a barrel of the firearm. A series of substantially parallel mounting ribs projects laterally from the elongate body. Each mounting rib has an outward facing surface and opposed sides that taper towards each other from the outward facing surface to the elongate body, such that a space between consecutive mounting ribs converges from the elongate body to the outward facing surfaces of the mounting ribs. A mounting assembly includes at least one connector receivable in a space between consecutive mounting ribs. A fastening mechanism is operable to secure the connector to the mounting ribs or to release the connector from the mounting ribs for infinite adjustment. A mount is arranged on the connector(s). The mount is configured for releasable connection to an ancillary device.