A sighting device is mountable to the side plate of a gun. The sighting device includes a light source (preferably a laser), a power source connectable to the light source. The sighting device is mounted to a gun, usually by being mounted to a side plate, which is then mounted to a gun. In one embodiment, the sighting device is mounted to the side plate by being screwed or bolted to it. In another embodiment, the sighting device includes a recess or channel that receives a rail, such as a dove-tail projection (or protrusion), formed on the side or vice versa. A side plate to which the sighting device can be attached and a gun including the sighting device are also disclosed.