I sell copper films, the folks that laser or water jet use what is called 1/2 hard copper, there are usually 4 grades Hard, 1/2 Hard  1/4 Hard and Soft, all will machine nicely except the soft grade, if you bend it it will crease, and work harden, they can be stamped out and even have emboss rings  for sealing , but can only be used once due to the crushing when torqued , this is why the best deal is to go through a builder and get your head or cylinder O ringed  correctly, cheaper to keep extra O rings in the tool box