Integrated optical sighting system for firearm

An illuminated reflex optical sighting system integrated directly into a firearm includes a lighting module comprising an illumination source mounted to a body of the firearm at a discrete first mounting location, an optical lens assembly mounted to the body of the firearm at a discrete second location spatially distanced from the first location, and a power source operably coupled to the illumination source. The illumination source is configured and operable to project a reticle onto a lens of the lens assembly for use in aiming the firearm. The illumination source and lens assembly are separately mounted to and independently removable from the body of the firearm thereby providing a low profile sighting system which substantially retains the aspects of the original firearm. The illumination source, power source, and lighting control circuitry may be housed inside the metal rear sight of the firearm in one embodiment.