MichaelG,Ady1, got all of Andy Ross's stuff printed out, including his book "Making Stirling Engines" (free down load 68 pages).
HomeUse, copper is not much use as a hot cap, it conducts heat too fast length wise, and scales up with oxide inside, and makes a bit of a mess, also the heating softens the metal, and it bulges, and bends. Just back from my tame TIGer, putting an end on a bit of stainless tube to make the hot cap, I'll take it back on Monday, it leaked like a sieve, the metal I tried for the end was too thin, at .015" just too difficult, although in the past he's managed half that thickness. Ian S C