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The word caliber (American English) or calibre (British English) comes from the Italian calibro, itself from the Arabic quâlib, meaning metal mold. It designates the interior diameter of a tube or the exterior diameter of a wire or rod.

In architecture, the caliber of a column is its diameter. In electricity, the caliber of an instrument of measure is the maximum value it can measure. In nautical parlance, the caliber of a chain is the diametre of the metal rod used to make each chain link. Agricultural produce is also often ranked by caliber (diameter), for instance olives, peas or eggs. In typography, the calibre of a font designates the size of the eye of a character, neglecting any risers or descenders.

In small arms, the caliber is the diameter of the inside of the barrel. This distance is measured from between the 'lands' in a rifled barrel, and is measured in inches. The caliber (abbreviated to cal) is expressed in either hundredths or thousandths of an inch, so .22 cal is 0.22 inches. Other quite popular calibers are .357, .38, .44 cal.

Outside England and the U.S., the caliber of a weapon is more frequently expressed in millimeters (mm). Though it is technically incorrect to say 9 mm cal, if the term caliber is used to mean 'barrel inside diameter', one could say 'the caliber is 9 mm'.

The caliber of a weapon is often informally used as a description of the type of arm it is. That is, a .45 cal pistol is called a '45', a 9 mm semi-automatic pistol is called just a '9 mm', a .380 caliber is called a '380', etc. This gives rise to the impression that the "cal" equals 1/100 or 1/1000 of an inch, whereas it is just an unfortunate figure of speech.

For historical reasons, the name of a cartridge often gives an imprecise indication of its caliber. As one example, the common 38 Special revolver actually fires a .357 inch diameter bullet.

Note that caliber is only a very poor approximation of the power of a cartridge. Other variables that come into play include bullet weight and shape, powder capacity of the cartridge casing, length of the barrel, and peak operating pressures.

Small arms range in bore size from approximately .177 cal to .50 cal. Arms used to hunt big game may be as large as .700 caliber. In historical times, through the middle of the 19th century, muskets and muzzle-loading rifles of .58 cal or larger were used.

In artillery pieces, caliber also refers to the length of the barrel, expressed as a multiple of the bore diameter. So the great guns of the Iowa class battleships are properly referred to as 16"/50 caliber as they have a 16 inch diameter bore and are 800 (50 times 16) inches (approx 20 m) long.

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Last updated: 02-06-2005 23:54:12
Last updated: 02-11-2005 17:47:38