In addition to the casting manuals mentioned, there are several other books you should keep an eye out for on the used book market. They are all out of print now (as far as I know).
Wolfe Publishing put out a book which is a compilation of numerous casting articles from "Handloader" magazine. The book is "The Art of Bullet Casting".
Wolfe also published 3 special magazines. I can't remember their exact titles, but they were something like "Cast Bullet Annual", then there was "Cast Bullets Vol II" and a third one with a similar name. These came out in the early 1990's, I think.
Finally, the NRA published a compilation of casting articles from the American Rifleman in a book called "Cast Bullets". They later published a 15 or 20 page addendum to this book.
All of these are worth getting, if you can find them. I think they are almost becoming collector items!