Calibre

Calibre, or CALIBER, is a technical name for the diameter of the bore of a firearm, whether a piece of ordnance or a small-arm. If the weapon is rifled its calibre is measured, not from the bottom of the grooves, but from the smooth surface between them, technically called the 'lands.' Ordnance firing solid shot were formerly denoted by the weight of each shot, as 24-pounder, 68-pounder, &c. ; mortars and shell-guns by their calibre, as 13-inch mortar, 10-inch shell-gun, &c. ; but now that all guns fire shell, this rule is not always observed. It has become usual to designate guns heavier than the 80-pounder, together with all howitzers and mortars, by their calibre, and lighter natures by the weight of the shell ; but in every case the weight of the gun itself is also specified, as the 17.8-inch gun of 100 tons, the 80-pounder of 5 tons. Machine Guns (q.v.) and rifles are always classified by their calibres.