In my opinion, the most comprehensive reference is Peter Alexander's The Gunsmith of Grenville County. It includes all the material in Buchelle's book and then some. The next book I would buy is Gunsmithing Tips & Projects, a compilation of Rifle magazine articles, for the articles by John Bivins. That is what I read and study these days along with the Journals of Historical Armsmaking Technology. After you have an idea what you are doing, John Bivins tells you how it is really done. He shared so much, it is a shame he was taken so soon.