Doc,I initially thought that having the hot cap thin all over in one carved out of a solid lump of 316 was the way to go, but since then I have decided thatalength of the hot cap about equal to the stroke at the hot end should be left at a little thicker, so .030", the rest about half that to ward the cool end to act as a heat dam, thinner the metal, slower the conduction of heat. If you make it too thin, the heat tends to cause the hot cap to droop, and wrinkle, mind you thats after years of use at maximum temperature.
Ian S C