Caliber

In guns, particularly firearms, caliber or calibre is the approximate internal diameter of the barrel, or the diameter of the projectile it fires, usually shown in millimeters, or in hundredths or thousandths of an inch.

In guns, particularly firearms, caliber or calibre is the approximate internal diameter of the barrel, or the diameter of the projectile it fires, usually shown in millimeters, or in hundredths or thousandths of an inch. When expressed in inches in writing or print, it is shown in terms of a decimal fraction: .45 caliber, for example. When the barrel diameter is given in inches, the abbreviation "cal" can be used. For example, a small-bore rifle with a diameter of 0.22 inches can be called a .22 or a .22 cal; however, the decimal point is generally dropped when spoken, making it a "twenty-two caliber" or a "two-two caliber" rifle. However, when caliber is expressed in millimeters, this is noted, as in, "9mm pistol."

In a rifled barrel, the distance is measured between opposing lands or grooves; groove measurements are common in cartridge designations originating in the United States, while land measurements are more common elsewhere. Good performance requires a bullet to closely match the groove diameter of a barrel to ensure a good seal.

While modern cartridges and cartridge firearms are generally referred to by the cartridge name, they are still lumped together based on bore diameter. For example, a firearm might be described as a '.30 caliber rifle', which could be any of a wide range of cartridges using a roughly .30-in projectile; or a ".22 rimfire", referring to any rimfire cartridge using a .22-cal projectile.

Firearm calibers outside the range of .17 to .50 (4.5 to 12.7 mm) exist, but are rarely encountered. Wildcat cartridges, for example, can be found in .10, .12, and .14 cal (2.5, 3.0, and 3.6 mm), typically used for short-range varmint hunting, where the high-velocity, lightweight bullets provide devastating terminal ballistics with little risk of ricochet. Larger calibers, such as .577, .585, .600, .700, and .729 (14.7, 14.9, 15.2, 17.8, & 18.5 mm) are generally found in proprietary cartridges chambered in express rifles or similar guns intended for use on dangerous game. The .950 JDJ is the only known cartridge beyond .79 caliber used in a rifle.

In some contexts, e.g. guns aboard a warship, "caliber" is used to describe the barrel length as multiples of the bore diameter. A "5-inch 50 calibre" gun has a bore diameter of 5 in (12.7 cm) and a barrel length of 50 times 5 in = 250 in (6.35 m)

In modern Union terms, only H&K still uses the term Caliber.

[Notes] Erica Olafson carries a .45 caliber Colt and uses it frequently. Admiral Stahl also carries a .45 colt. The Colt carried by Phil Decker is no longer a weapon of human techj origing. Peter Baker is know to carry a Smith & Wesson revolver S&W 500 in .50 cal. He also has a single handgun in 50 BMG. Other famous gun owners include Admiral McElligott (Enfield rifle), Rex Schwartz - extensive collection