I was doing a little searching on it last night and was beginning to think it was a mythical book as I couldn't even find anything on it at the Library of Congress. I went thru my old copies of Muzzleloader Magazine and low and behold found an advertisement for it the May/June 1986 issue.
Have you tried asking on any of the Muzzleloader Forums? That might be a better place since it the book was aimed at them.