Hi,
For a history of the flintlock mechanism, Torsten Lenk's "The Flintlock" is still the classic reference. For a history of the American long rifle, Joe Kindig's "Thoughts on the Kentucky Rifle in its Golden Age" and Henry Kaufmann's "The Pennsylvania-Kentucky Rifle" are still good reads but dated, although there is a new annotated edition of Kindig's book. Both books have chapters discussing the history of the rifle and the gunsmith's trade but the best books dealing with how gun makers worked are probably the 2 volumes by Bob Lienemann on Moravian gun making. They focus on 18th century Moravian gun makers but provide more detail on how the trade was run than almost any other source. George Shumway's two volumes "Rifles in Colonial America" show many early guns and illustrate the regional styles and some of the history. Finally, the short movie available on You Tube called "The Gunsmith of Colonial Williamsburg" is a nice introduction to how they were made in the 18th century.
dave