I won't repeat any of the other excellent recommendations. But anything written by Walter Winans is worth reading. He's the only man to win Olympic Gold for art. And rifle shooting. The punch line being that he won the Art gold with a sculpture...Winans was primarily a pistol shooter and a painter with watercolors (he illustrated most of his books himself). Fantastically gifted writer, too.
Other books would include Ned Roberts' book on the muzzle-loading rifle, Geoffery Boothroyd's "The Handgun" (a little dated now, but very complete), "Small Arms of the World", and "The British Duelling Pistol". Tim Mullin wrote three books (now sadly out of print) reviewing military rifles, pistols, and full-auto weapons that are really outstanding.