Abstract: The safety device of the present invention comprises a longitudinally extensible element adapted to be placed in one chamber of a revolver type gun so that the cylinder can be closed and the device positioned to extend through the chamber into the bore of the barrel to prevent the cylinder from rotating thus preventing the gun from being operated. The device is designed so that it must be rotated within the gun barrel to remove it from the gun so that individuals not knowing how the device operates cannot easily remove the device from the gun.