The second law revision in 1977 is even stricter. It prohibited the use of hard metal other than soft metal (hardness measured by Brinell scale (10/500) 91 HB or less) like zinc alloy in main parts of metal modelguns. The metal model handguns must have completely sealed barrel and added a hardened steel rod molded inside softer metal barrel to prevent attempts of modification and making it pass-through. Front of cylinder chamber of revolvers must be blocked. The barrel and frame of metal model handguns must not be separable to prevent the interchange of the barrel. This new regulation prohibits further production of many full metal model handguns with separable barrel and slide. The ASGK manage the safety approval and the SMG (Safe Model Gun) mark replaced the SM mark on the metal models to identify the models meeting the new regulation.