A method of aligning the boresight of a weapon in which the method compri mounting an aiming light on a boresight mechanism that is attached to the weapon. A canister, which has the same diameter and general shape of a cartridge that the weapon fires and has a light emitting source and beam width narrowing projecting lens therein, is inserted in the breech of the weapon to provide a narrow beam boresight light along the true boresight of the weapon. Battery leads are connected to the light emitting source with the ground lead secured to an end cap of the canister and the hot lead connected to the light emitting source. The battery is located in the aiming light housing. The operator aligns the aiming light with the boresight of the weapon appropriately adjusting the aiming light beam with respect to the boresight light beam, and observing the position of the reflected lights from a target through a viewing scope. The canister may be pulled out of the breech by pulling on the battery leads.