The boresight laser aiming system for firearms provides a laser aiming beam through the mechanical action (20), chamber, and barrel (36) of the operable firearm (10) and through a specially configured live rimfire cartridge within the chamber, enabling a marksman to place the laser upon the target and fire the weapon simultaneously. The laser device (12) may be installed concentrically with a light passage through the bolt (22), hammer, or other mechanism of the firearm, or may be offset with the light path guided by one or more reflective mirrors, prisms, etc. The firearm may comprise a rifle (10), semiautomatic pistol, revolver, etc. The live cartridge has concentric inner and outer tubes defining a toroidal explosive charge-containing chamber therebetween and a light passage through the innermost tube, and a bullet having a passage therethrough allowing light to pass through the live cartridge assembly when placed in the firearm chamber.