The
gauge of a
firearm is a
unit of measurement used to express the
diameter of the
barrel. Gauge is determined from the weight of a solid
sphere of
lead that will fit the bore of the firearm, and is expressed as the
multiplicative inverse of the sphere's weight as a fraction of a
pound (e.g., a th pound ball fits a 12-gauge bore). Thus there are twelve 12-gauge balls per pound (etc.). The term is related to the measurement of
cannon, which were also measured by the weight of their
iron round shot; an
8 pounder would fire an ball.