Explosively-powered weapons are frequently called gunnery. Small arms are usually called firearms, side arms or infantry arms, or, in earlier times, muskets. In strict military terms, the word gun does not refer to small firearms, but to large artillery pieces like cannon that generally require a crew for their operation.
Stahl Coastal Defense Gun.
Photo: © 2002 Aeragon; all rights reserved.
US Army Ordnance Corps Museum.
Aberdeen Proving Ground, Maryland.
A general rule-of-thumb to distinguish between firearms and guns is that firearms are weapons of less than .60 inch caliber (0.6-inch or 15.24-mm bore) and all gauges of shotguns are classed as firearms. Nevertheless, the distinction between small arms and artillery is fairly vague and in common usage the term gun is frequently used to describe firearms. Several modern weapons with the word gun in their names such as shotgun and machine gun have further confused the distinction between firearms and guns.
A Gun For Every Job - Buy War Savings - Hit the Target; Circa 1944.
W.F.P.353 Issued by the National Savings Committee, London;
Scottish Savings Committee, Edinburgh;
Ulster Savings Committee, Belfast.
Crown Copyright Reserved.
Printed for Her Majesty's Stationery Office
by Wm. Brown and Company, Limited, London.
National Archives and Records Administration.
Still Picture Branch; College Park, Maryland.