In guns, particularly firearms, caliber is the specified nominal internal diameter of the gun barrel bore – regardless of how or where the bore is measured and whether the finished bore matches that specification. It is measured in inches or in millimeters. In the United States it is expressed in hundredths of an inch; in the United Kingdom in thousandths; and elsewhere in millimeters. For example, a "45 caliber" firearm has a barrel diameter of roughly 0.45 inches (11 mm). Barrel diameters can also be expressed using metric dimensions. For example, a "9 mm pistol" has a barrel diameter of about 9 millimeters. Since metric and US customary units do not convert evenly at this scale, metric conversions of caliber measured in decimal inches are typically approximations of the precise specifications in non-metric units, and vice versa.
Rimfire ammunition is a type of firearm metallic cartridge whose primer is located within a hollow circumferential rim protruding from the base of its casing. When fired, the gun's firing pin will strike and crush the rim against the edge of the barrel breech, sparking the primer compound within the rim, and in turn ignite the propellant within the case. Invented in 1845, by Louis-Nicolas Flobert, the first rimfire metallic cartridge was the .22 BB Cap cartridge, which consisted of a percussion cap with a bullet attached to the top. While many other different cartridge priming methods have been tried since the 19th century, only rimfire and the later centerfire cartridges survive to the present day with regular usages. The .22 Long Rifle rimfire cartridge, introduced in 1887, is by far the most common ammunition in the world today in terms of units sold.
The .22 Long Rifle or simply .22 LR or 22 is a long-established variety of .22 caliber rimfire ammunition originating from the United States. It is used in a wide range of rifles, pistols, revolvers, smoothbore shotguns, and submachine guns.
The .45 Colt (11.43×33mmR), is a rimmed, straight-walled, handgun cartridge dating to 1872. It was originally a black-powder revolver round developed for the Colt Single Action Army revolver. This cartridge was adopted by the U.S. Army in 1873 and served as an official US military handgun cartridge for 14 years.
The .223 Remington is a rimless, bottlenecked rifle cartridge. It was developed in 1957 by Remington Arms and Fairchild Industries for the U.S. Continental Army Command of the United States Army as part of a project to create a small-caliber, high-velocity firearm. The .223 Remington is considered one of the most popular common-use cartridges and is currently used by a wide range of semi-automatic and manual-action rifles as well as handguns.
The .44 Remington Magnum, also known as .44 Magnum or 10.9x33mmR, is a rimmed, large-bore cartridge originally designed for revolvers and quickly adopted for carbines and rifles. Despite the ".44" designation, guns chambered for the .44 Magnum round, and its parent, the .44 Special, use 0.429 in (10.9 mm) diameter bullets. The .44 Magnum is based on the .44 Special case but lengthened and loaded to higher pressures for greater velocity and energy.
The 7×57mm Mauser is a first-generation smokeless powder rimless bottlenecked rifle cartridge. It was developed by Paul Mauser of the Mauser company in 1892 and adopted as a military cartridge by Spain in 1893. It was subsequently adopted by several other countries as the standard military cartridge, and although now obsolete as a military cartridge, it remains in widespread international use as a sporting round. The 7×57 Mauser was a popular stalking cartridge and sporting rifles in this chambering were made by the famous British riflemakers, such as John Rigby, Holland and Holland, Westley Richards and others. British cartridge nomenclature designated caliber in inches, and the cartridge was known as the .275 bore after the measurement of a 7 mm rifle's bore across the lands.
The 5.45×39mm cartridge is a rimless bottlenecked intermediate cartridge. It was introduced into service in 1974 by the Soviet Union for use with the new AK-74. The 5.45×39mm gradually supplemented and then largely replaced the 7.62×39mm cartridge in Soviet and Warsaw Pact service as the primary military service rifle cartridge.
The .458 Winchester Magnum is a belted, straight-taper cased, big five game rifle cartridge. It was introduced commercially in 1956 by Winchester and first chambered in the Winchester Model 70 African rifle. It was designed to compete against the .450 Nitro Express and the .470 Nitro Express cartridges used in big bore British double rifles. The .458 Winchester Magnum remains one of the most popular large game cartridges, and most major ammunition manufacturers offer a selection of .458 ammunition.
The .257 Weatherby Magnum is a .257 caliber (6.53 mm) belted bottlenecked cartridge. It is one of the original standard length magnums developed by shortening the .375 H&H Magnum case to approx. 2.5 in (64 mm). Of the cartridges developed by Roy Weatherby, the .257 Weatherby Magnum was known to have been his favorite, and the cartridge currently ranks third in Weatherby cartridge sales, after the .30-378 Weatherby Magnum and the .300 Weatherby Magnum.
The 6mm PPC, or 6 PPC as it is more often called, is a centerfire rifle cartridge used almost exclusively for benchrest shooting. It is one of the most accurate cartridges available at distances of up to 300 meters. This cartridge's accuracy is produced by a combination of its stout posture, being only 31 mm (1.22 in) long, and aggressive shoulder angle of 30 degrees. Its primary use has been benchrest shooting matches since the 1980s.
The .444 Marlin (10.9×57mmR) is a rifle cartridge designed in 1964 by Marlin Firearms and Remington Arms. It was designed to fill in a gap left by the older .45-70 when that cartridge was not available in any new lever-action rifles; at the time it was the largest lever-action cartridge available. The .444 resembles a lengthened .44 Magnum and provides a significant increase in velocity. It is usually used in the Marlin 444 lever-action rifle.
The .338 Winchester Magnum is a .338 in (8.6 mm) caliber, belted, rimless, bottlenecked cartridge introduced in 1958 by Winchester Repeating Arms. It is based on the blown-out, shortened .375 H&H Magnum. The .338 in (8.6 mm) is the caliber at which medium-bore cartridges are considered to begin. The .338 Winchester Magnum is the first choice among professional brown bear guides in Alaska to back up clients where a powerful stopping caliber is required on charging bears. It is also the most popular medium-bore cartridge in North America and has the most widely available choice in rifles among medium bore rifles. The action length is the same as a .30-06, and most major rifle manufacturers in the United States chamber rifles for the cartridge including the semi-automatic Browning BAR Mk II Safari, making it a very powerful combination against charging dangerous game. The cartridge was intended for larger North American big-game species and has found use as for the hunting of thin-skinned African plains-game species.
The .416 Remington Magnum is a .416 caliber (10.57 mm) cartridge of belted bottlenecked design. The cartridge was intended as a dangerous game hunting cartridge and released to the public in 1989. The cartridge uses the case of the 8 mm Remington Magnum as a parent cartridge. When the cartridge was released in 1988, author Frank C. Barnes considered the .416 Remington Magnum to be the "most outstanding factory cartridge introduced in decades".
The .56-56 Spencer was an American black powder rifle cartridge.
The .475 No 2 Nitro Express is a British rifle cartridge developed by Eley Brothers in the early 20th century.
The 6 bore, also known as the 6 gauge, is an obsolete caliber that was used commonly in 19th-century black-powder firearms.
The .476 Enfield, also known as the .476 Eley, .476 Revolver, and occasionally .455/476, is a British centrefire black powder revolver cartridge. The Enfield name derives from the location of the Royal Small Arms Factory at Enfield Lock, the armoury where British military small arms were produced, while Eley was a British commercial brand. Used in the Enfield Mk II revolver, the Mk III variant was introduced by the British Army in 1881, supplanting the earlier .476 Enfield Mark I and II cartridges, which in turn had replaced the .450 Adams cartridges, all of which also used black powder propellant.
The .25-21 Stevens was an American centerfire rifle cartridge.
The .500 S&W Magnum or 12.7×41mmSR is a .50 caliber semi-rimmed revolver cartridge developed by Cor-Bon in partnership with the Smith & Wesson "X-Gun" engineering team for use in the Smith & Wesson Model 500 X-frame revolver and introduced in February 2003 at the SHOT Show. From its inception, it was intended to be the most powerful handgun cartridge to date, with the capacity to harvest all North American game species. While more powerful handgun cartridges, such as the .500 Bushwhacker, have emerged since, they are only available in custom firearms at this time, and the .500 S&W remains the most powerful production handgun cartridge.
