A great classic that was reprinted a few years ago, but again seems to be somewhat rare is the two volume "International Armament" by Johnson and Lockhoven.
This was written with the support of the famous (infamous??) Sam Cummings of Interarmco or Interarms.
Volume One covers pistols, revolvers, single shot rifles, and bolt rifles.
Volume Two covers semi and full auto rifles, submachine guns, light machine guns, and heavy machine guns.
This is primarily a history of the arms with only short disassembly instructions. It covers when they were made, who made them, typical markings, and a short history of where they were used.
At one time, this was considered to be the "standard reference" for military small arms.
Originals and reprints show up on Ebay and at book sellers from time to time.