There are so many books on Gunsmithing that it would be next to impossible to recommend just one as a "Bible" on Gunsmithing. Here's a few from my collection that I've collected over the years:
Gunsmithing Tips and Projects by Wolfe Publishing
The Modern Gunsmith Vol 1 and 2 by Howe
Professional Gunsmithing by Howe
Gunsmithing by Roy Dunlap
NRA Firearms Assembly
More modern books would include:
Gunsmithing Rifles by Sweeney
Gunsmithing Shotguns by Sweeney
Gunsmithing Pistols and Revolvers by Sweeney
Jerry Kuhnhausen has several manuals out that include Ruger Single Action Revolvers plus shop manuals on S&W Revolvers, The Colt .45 automatic, Colt Double Action Revolvers, Ruger Double Action Revolvers plus more on long guns too. I found most of my early books at used book stores and had a lot of fun doing so. There are quite a few on line sites that offer these books too.
Good luck in your search for "the" Gunsmithing book.
Mike