Abstract: A chamber and bore lock for a firearm includes a rod adapted for receipt within the barrel bore of the firearm. One end of the rod has a fixed plug with an abutting O-ring. A pair of sleeves are received upon the rod with an O-ring therebetween. A threaded cap engages an end of the rod at the muzzle of the firearm, such that threaded movement of the cap draws the plug toward the cap, urging the sleeves into compressing and radially deforming engagement with the O-rings which engage inner circumferential surfaces of the barrel bore and firing chamber of the firearm.