Abstract: A diagonally split sleeve affords a pair of wedges at least one of which is laterally displaced when the wedges are urged together. By locating the wedges in the firing chamber of a gun, the gun is rendered useless; and by positioning the wedges adjacent the tapered throat of the firing chamber, the lateral displacement, or expansion, can be taken advantage of to prevent unauthorized removal of the device. A cylinder lock and special cams attached to a tube and coaxial actuating rod extending through the gun barrel from the muzzle to the firing chamber serve to position and actuate the wedges only in response to operation of the lock key.