Rolf.
Very nice job. I am very impressed. You have a good mind and are no doubt a master craftsman. You should try serrosafe for casting a die. You can get that metal in any melting range and it is hard. It can also be used for many other things. I keep a few pounds of it around all the time. Zink will also work but melts around 800° You can cast zink in silicone molds. Your my kind of ground up builder.