Thanks very much for the info, Curious. The info you gave will be most helpful to me. I do have data from two other 9.3s (one from Germany) that do not have the step, and the barrel just starts tapering directly from the rear sight base and is .9 there. I like the step version better. So I will use the dimensions you gave. I have actually made these before but I basically guessed at the dimensions. One note is that all German military Mausers also use a .900 diameter for the rear sight base, so that must be a magic number.
Thanks. Happy New Year.