A laser bore sight and method for a gun such as a rifle is provided which includes a mandrel with a laser affixed and an arbor for threadably receiving the mandrel. The arbor has a slotted conical well and a threaded shaft in communication therewith so that tightening the mandrel into the arbor will expand the outer diameter of the arbor to hold it firmly within the bore of the gun barrel while it is being sighted. To remove the laser bore sight the mandrel is rotated in an opposite direction and the arbor and mandrel are then easily removed.