An upgrade kit for an assault rifle, the rifle comprising a rear trunnion and a barrel, the kit comprising a mounting rail assembly adapted to provide steady and tight attachment to the barrel, an ambidextrous charging handle assembly adapted to be installed on the right or the left side of the rifle, at substantially the same location along the longitudinal axis. The charging handle assembly comprises a modified bolt carrier having a perforation, an installation rod having a first gap, and the installation rod corresponding in shape to the perforation in the bolt carrier. The charging handle is configured to be gripped by a user, and an intermediate section having a second gap, and connected to the installation rod and to the charging handle.
