I am going to recommend against buying the e-book as they are either incompatable with some computers or Amazon.com is unable to fullfill their obligations. At best, attempting to buy the E-book is a gamble. There also appear to be some problems with their online sales of hard bound and paperback books. One alternative to their system is Barnes and Noble:
http://search.barnesandnoble.com/booksearch/results.asp?WRD=percussion+pistols+and+revolvers&z=y
They do not handle e-books
http://search.barnesandnoble.com/booksearch/results.asp?WRD=percussion+pistols+and+revolvers&z=y
They do not handle e-books