Abstract: An apparatus to enable accurate sight adjustment of rifles consisting of a mounting assembly formed as a body of revolution and having a head portion, a mandrel portion and a cylinder portion including an expansion tube. A suitable light spot generating device is mounted in axial alignment with the mounting assembly head portion and the mandrel and cylinder portions may be inserted in the muzzle end of the gunbore and secured in axial position so that the light beam projected to a distant target may provide sighting reference for an associated scope of mechanical sight.