There are many I'm afraid.. The Digest books help with those unusual specimens and The books by Patrick Sweeney(sp.) are great. All the NRA gunsmithing guides have great info and Nontes 'the Book of the 45' if a wealth of info. The Kinks books of course.. I regularly haunt EBay and book shops and stores, auctions and sales looking for more information.. As is the norm Brownells has a great selection some of which are fairly specific such as tomes on welding and machine tools. The machinists bedside reader series are also good basic info even if you don't have a lathe or mill. Jerry Kuhnhausen's books are the greatest, if he has one for the piece your going to work on..the 45 1911 series (2 vols,.) is extraordinary!! And of course you can always come back here and ask some of the knowledgeable folks who haunt these strings... learning, for a gunsmith, is never though.