The most comprehensive, authoritative guide to identifying firearms includes:
Pistols, revolvers, submachine guns, machine guns, bolt-action and automatic rifles, and shotguns Technical specifications Manufacturers and brand names index Firearm safety information More than 400 photographs
This book showed me a lot of guns some of them I knew and others I didn't know but now I know a lot more guns. It also told me different ways that receivers and actions work and who the manufactures are and the different countries that make the guns.
Jane's gun guides have been the gold standard in weapon identification since there was a gold standard for it. Good descriptions and clear pictures and drawings of weapons and their end use and who uses them.