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In
gun
A gun is a ranged weapon designed to use a shooting tube (gun barrel) to launch projectiles. The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns/cannons, spray guns for painting or pressure washing, pr ...
s, particularly
firearm
A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions).
The first firearms originated in 10th-century China, when bamboo tubes ...
s, caliber (or calibre; sometimes abbreviated as "cal") is the specified nominal internal
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
of the
gun barrel
A gun barrel is a crucial part of gun-type weapons such as small firearms, artillery pieces, and air guns. It is the straight shooting tube, usually made of rigid high-strength metal, through which a contained rapid expansion of high-pressure ...
bore – regardless of how or where the bore is measured and whether the finished bore matches that specification. It is measured in
inch
Measuring tape with inches
The inch (symbol: in or ″) is a unit of length in the British imperial and the United States customary systems of measurement. It is equal to yard or of a foot. Derived from the Roman uncia ("twelfth") ...
es 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 . 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.
In a
rifled
In firearms, rifling is machining helical grooves into the internal (bore) surface of a gun's barrel for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting to stabilize the proj ...
barrel, the distance is measured between opposing
lands
Land is the solid surface of the Earth that is not covered by water.
Land, lands, The Land, or the Lands may also refer to:
Entertainment and media Film
* ''Land'' (1987 film), a British television film by Barry Collins
* ''Land'' (2018 film), ...
or between opposing
grooves; groove measurements are common in cartridge designations originating in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, while land measurements are more common elsewhere in the world. Measurements "across the grooves" are used for maximum precision because
rifling
In firearms, rifling is machining helical grooves into the internal (bore) surface of a gun's barrel for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting to stabilize the pro ...
and the specific caliber so-measured is the result of final machining process which cuts grooves into the rough bore, leaving the "lands" behind.
Good performance requires a concentric, straight bore that accurately centers the projectile within the barrel, in preference to a "tight" fit which can be achieved even with off-center, crooked bores that cause excessive friction, fouling and an out-of-balance, wobbling projectile in flight.
Calibers fall into four general categories by size:
* miniature-bore historically refers to calibers with a diameter of .22 inch or smaller
*
small-bore Small-bore refers to calibers with a diameter of .32 inches or smaller. It may also refer to small-bore rifle competition. The medium-bore refers to calibers with a diameter between .33 inches up to .39 inches and large-bore refers to calibers with ...
refers to calibers with a diameter of .32 inches or smaller
* medium-bore refers to calibers with a diameter of .33 inches to .39 inches
* large-bore refers to calibers with a diameter of .40 inches or larger
There is much variance in the use of the term "small-bore", which over the years has changed considerably, with anything under .577 caliber considered "small-bore" prior to the mid-19th century.
Cartridge naming conventions
While modern firearms are generally referred to by the name of the
cartridge the gun is chambered for, they are still categorized together based on bore diameter. For example, a firearm might be described as a "
30 caliber
The 7.62 mm caliber is a nominal caliber used for a number of different cartridges. Historically, this class of cartridge was commonly known as .30 caliber, the imperial unit and customary unit equivalent, and was most commonly used for i ...
rifle", which could accommodate any of a wide range of cartridges using a roughly projectile; or as a "22 rimfire", referring to any
rimfire firearms firing cartridges with a
22 caliber projectile. However, there can be significant differences in nominal bullet and bore dimensions, and all cartridges so "categorized" are not automatically identical in actual caliber.
For example,
303 British
The .303 British (designated as the 303 British by the C.I.P. and SAAMI) or 7.7×56mmR, is a calibre rimmed rifle cartridge. The .303 inch bore diameter is measured between rifling lands as is the common practice in Europe which follows the ...
firearms and projectiles are often "categorized" as ".30-caliber" alongside several dozen U.S. "30-caliber" cartridges despite using bullets of .310–.312″ diameter while all U.S "30-caliber" centerfire rifle cartridges use a common, standard .308″ bullet outside diameter. Using bullets larger than design specifications causes excessive pressures, while undersize bullets cause low pressures, insufficient muzzle velocities and fouling that will eventually lead to excessive pressures.
Makers of early cartridge arms had to invent methods of naming cartridges since no established convention existed then.
One of the early established cartridge arms was the
Spencer repeating rifle
The Spencer repeating rifles and carbines were 19th-century American lever-action firearms invented by Christopher Spencer. The Spencer was the world's first military metallic-cartridge repeating rifle, and over 200,000 examples were manufacture ...
, which
Union
Union commonly refers to:
* Trade union, an organization of workers
* Union (set theory), in mathematics, a fundamental operation on sets
Union may also refer to:
Arts and entertainment
Music
* Union (band), an American rock group
** ''Un ...
forces used in the
American Civil War
The American Civil War (April 12, 1861 – May 26, 1865; also known by other names) was a civil war in the United States. It was fought between the Union ("the North") and the Confederacy ("the South"), the latter formed by states th ...
. It was named based on the
chamber
Chamber or the chamber may refer to:
In government and organizations
* Chamber of commerce, an organization of business owners to promote commercial interests
*Legislative chamber, in politics
* Debate chamber, the space or room that houses delib ...
dimensions, rather than the bore diameter, with the earliest cartridge called the "No. 56 cartridge", indicating a chamber diameter of .56 in; the bore diameter varied considerably, from .52 to .54 in. Later various
derivatives
The derivative of a function is the rate of change of the function's output relative to its input value.
Derivative may also refer to:
In mathematics and economics
* Brzozowski derivative in the theory of formal languages
* Formal derivative, an ...
were created using the same basic cartridge, but with smaller-diameter bullets; these were named by the cartridge diameter at the base and mouth. The original No. 56 became the .56-56, and the smaller versions, .56-52, .56-50, and .56-46. The 56-52, the most common of the new calibers, used a 50-cal bullet.
Other black powder-era cartridges used naming schemes that appeared similar, but measured entirely different characteristics;
45-70
The .45-70 rifle cartridge, also known as the .45-70 Government, was developed at the U.S. Army's Springfield Armory for use in the Springfield Model 1873, which is known to collectors as the "Trapdoor Springfield." The new cartridge was a replac ...
,
44-40
The .44-40 Winchester, also known as .44 Winchester, .44 WCF (Winchester Center Fire), and .44 Largo (in Spanish-speaking countries) was introduced in 1873 by the Winchester Repeating Arms Company. It was the first metallic centerfire cartridge man ...
, and
32-20
3 (three) is a number, numeral and digit. It is the natural number following 2 and preceding 4, and is the smallest odd prime number and the only prime preceding a square number. It has religious or cultural significance in many societie ...
were designated by bullet diameter to hundredths of an inch and standard
black powder
Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). Th ...
charge in
grain
A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...
s. Optionally, the bullet weight in grains was designated, e.g. 45-70-405.
[ This scheme was far more popular and was carried over after the advent of early ]smokeless powder
Finnish smokeless powderSmokeless powder is a type of propellant used in firearms and artillery that produces less smoke and less fouling when fired compared to gunpowder ("black powder"). The combustion products are mainly gaseous, compared to a ...
cartridges such as the 30-30 Winchester
The .30-30 Winchester/.30 Winchester Center Fire cartridge was first marketed in 1895 for the Winchester Model 1894 lever-action rifle.[22 Long
22 Long is a variety of 22 caliber (5.6 mm) rimfire ammunition. The 22 Long is the second-oldest of the surviving rimfire cartridges, dating back to 1871, when it was loaded with a 29 grain (1.9 g) bullet and 5 grains (0.32 g) of black pow ...]
. Later developments used terms to indicate relative power, such as .44 Special
The .44 Smith & Wesson Special, also commonly known as .44 S&W Special, .44 Special, .44 Spl, .44 Spc, (pronounced "forty-four special"), or 10.9x29mmR is a smokeless powder center fire metallic revolver cartridge developed by Smith & Wesson in 1 ...
and .44 Magnum. Variations on these methods persist today, with new cartridges such as the 204 Ruger
The .204 Ruger is a centerfire rifle cartridge developed by Hornady and Ruger. At the time of its introduction in 2004, the .204 Ruger was the second-highest velocity commercially produced ammunition and the only centerfire cartridge produced c ...
and 17 HMR
.17 Hornady Magnum Rimfire, commonly known as the .17 HMR, is a rimfire rifle cartridge developed by Hornady in 2002. It was developed by necking down a .22 Magnum case to take a .17 caliber (4.5 mm) projectile. Commonly loaded with a 17 g ...
(Hornady Magnum Rimfire).
Metric diameters for small arms refer to cartridge dimensions and are expressed with an "×" between the bore diameter and the length of the cartridge case; for example, the 6.5×55mm Swedish cartridge has a bore diameter of 6.5 mm and a case length of 55 mm.[
The means of measuring a rifled bore varies, and may refer to the diameter of the lands or the grooves of the rifling.][ For example, the ]257 Roberts
The .257 Roberts, also known as .257 Bob, is a medium-powered .25 caliber rifle cartridge. It has been described as the best compromise between the low recoil and flat trajectory of smaller calibers such as the 5 mm (.22") and 6 mm (.24"), and t ...
and 250 Savage
5 (five) is a number, numeral and digit. It is the natural number, and cardinal number, following 4 and preceding 6, and is a prime number. It has attained significance throughout history in part because typical humans have five digits on eac ...
both use a .257 inch projectile; both 250 Savage and 257 Roberts rifle bores have a .250 inch land diameter and .257 inch groove diameter. The .308 Winchester
The .308 Winchester is a smokeless powder rimless bottlenecked rifle cartridge widely used for hunting, target shooting, police, military, and personal protection applications globally. It is similar but not identical to the 7.62×51mm NATO ...
is measured across the grooves and uses a .308-in diameter (7.82-mm) bullet; the military-specification version is known as 7.62 × 51 mm NATO, so called because the bore diameter measured between the lands is 7.62 mm, and the cartridge has a case 51 mm long.
Rifle caliber and cartridge conversions
Converting a rifle to fire a different cartridge in the same bore diameter, often involves merely re-chambering the barrel to the new cartridge dimensions, if the rim diameter of the new cartridge matches that of the old cartridge. Converting a rifle to fire a different cartridge in a different caliber and bore as what it initially was, means that the barrel of the rifle will also need to be changed. Because many competitive precision rifle shooters often shoot thousands of rounds per year both for practice and competitions, and they more often reach the end of their barrel life, whereby the rifling
In firearms, rifling is machining helical grooves into the internal (bore) surface of a gun's barrel for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting to stabilize the pro ...
is worn down to a point where a rifle loses some of its accuracy
Accuracy and precision are two measures of ''observational error''.
''Accuracy'' is how close a given set of measurements (observations or readings) are to their ''true value'', while ''precision'' is how close the measurements are to each other ...
, the choice to make a caliber or cartridge change is often done at the same time as when a new rifle barrel
A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, ...
is fitted to the rifle by a gunsmith
A gunsmith is a person who repairs, modifies, designs, or builds guns. The occupation differs from an armorer, who usually replaces only worn parts in standard firearms. Gunsmiths do modifications and changes to a firearm that may require a very h ...
. There are a few important factors to consider when converting a rifle to a different caliber or cartridge. The action of the rifle should be long enough to contain the new cartridge, the magazine should also be able to hold the new cartridge, the bolt face should be the correct diameter and the extractor the correct size to hold the head of the new cartridge. The most common of these caliber conversions on rifles, are usually done to change from a parent cartridge to a new cartridge based on it, like when converting a rifle to a 6.5 mm Creedmoor from a 308 Winchester
The .308 Winchester is a smokeless powder rimless bottlenecked rifle cartridge widely used for hunting, target shooting, police, military, and personal protection applications globally. It is similar but not identical to the 7.62×51mm NATO ca ...
on which it is based.
Metric and US customary
The following table lists some of the commonly used calibers where both metric and US customary units are used as equivalents. Due to variations in naming conventions, and the whims of the cartridge manufacturers, bullet diameters can vary widely from the diameter implied by the name. For example, a difference of 0.045 in (1.15 mm) occurs between the smallest and largest of the several cartridges designated as ".38 caliber".
Shotguns
Shotguns are classed according to gauge, a related expression. The gauge of a shotgun refers to how many lead spheres, each with a diameter equal to that of the bore, amount to one pound (approximately 454 grams) in weight. In the case of a 12-gauge shotgun, it would take 12 spheres the size of the shotgun's bore to equal a pound. A numerically larger gauge indicates a smaller barrel: a 20-gauge shotgun requires more spheres to equal a pound; therefore, its barrel is smaller than the 12-gauge. This metric is used in Russia as "caliber number": e.g., "shotgun of the 12 caliber." The 16th caliber is known as "lordly" (russian: барский). While shotgun bores can be expressed in calibers (the .410 bore shotgun is in fact a caliber measure of .41 caliber 0.4 mm,[ unlike with rifles the actual bore diameter of a smoothbore shotgun varies significantly down the length of the barrel due to various chokes (and sometimes back-boring).
In the United Kingdom, "gauge" is referred to as "bore" and in the United States "bore" is referred to as "gauge", e.g. a "12-bore or gauge shotgun" has a bore or gauge that can accommodate a lead sphere weighing 1/12th of a pound.
]
Caliber as measurement of length
The length of artillery barrels (muzzle to breech) has often been described in terms of multiples of the bore diameter e.g. a 4-inch gun of 50 calibers (written 4" L/50 or 4"/50) would have a barrel 4 in × 50 = 200 in long. A 16-inch gun of 50 calibers (16" L/50) has a barrel length of 50 × 16 = 800 in (66 ft 8 in).
Both 14-in and 16-in navy guns were common in World War II. The British Royal Navy insisted on 50-cal guns on ships as it would allow shells to travel at an initial velocity of up to 1,800 mph (2,897 km/h) to a distance of 26 mi (42 km).
Pounds as a measure of cannon bore
Smoothbore cannon
A cannon is a large- caliber gun classified as a type of artillery, which usually launches a projectile using explosive chemical propellant. Gunpowder ("black powder") was the primary propellant before the invention of smokeless powder ...
and carronade
A carronade is a short, smoothbore, cast-iron cannon which was used by the Royal Navy. It was first produced by the Carron Company, an ironworks in Falkirk, Scotland, and was used from the mid-18th century to the mid-19th century. Its main func ...
bores are designated by the weight in imperial pounds of spherical solid iron shot of diameter to fit the bore. Standard sizes are 6, 12, 18, 24, 32, and 42 pounds, with some 68-pound weapons, and other nonstandard weapons using the same scheme. See Carronade#Ordnance.
From about the middle of the 17th century until the middle of the 19th century, measurement of the bore of large gunpowder weapons was usually expressed as the weight of its iron shot in pounds. Iron shot
Shot may refer to:
Arts, entertainment, and media
* ''Shot'' (album), by The Jesus Lizard
*''Shot, Illusion, New God'', an EP by Gruntruck
*'' Shot Rev 2.0'', a video album by The Sisters of Mercy
* "Shot" (song), by The Rasmus
* ''Shot'' (2017 f ...
was used as the standard reference because iron was the most common material used for artillery ammunition during that period, and solid spherical shot the most common form encountered. Artillery was classified thereby into standard categories, with 3-pdr., 4-pdr., 6-pdr., 8-pdr., 9-pdr., 12-pdr., 18-pdr., 24-pdr., and 32-pdr. being the most common sizes encountered, although larger, smaller and intermediate sizes existed.
In practice, though, significant variation occurred in the actual mass of the projectile for a given nominal shot weight. The country of manufacture is a significant consideration when determining bore diameters. For example, the French livre
LIVRE (, L), previously known as LIVRE/Tempo de Avançar (, L/TDA), is a green political party in Portugal founded in 2014.
Its founding principles are ecology, universalism, freedom, equity, solidarity, socialism and Europeanism. Its symbol ...
, until 1812, had a mass of 489.5 g whilst the contemporary English (avoirdupois
The avoirdupois system (; abbreviated avdp.) is a measurement system of weights that uses pounds and ounces as units. It was first commonly used in the 13th century AD and was updated in 1959.
In 1959, by international agreement, the definiti ...
) pound massed approximately 454 g. Thus, a French 32-pdr at the Battle of Trafalgar
The Battle of Trafalgar (21 October 1805) was a naval engagement between the British Royal Navy and the combined fleets of the French and Spanish Navies during the War of the Third Coalition (August–December 1805) of the Napoleonic Wars (180 ...
threw a shot with more mass than an English 32-pdr.
Complicating matters further, muzzle-loaded weapons require a significant gap between the sides of the tube bore and the surface of the shot. This is necessary so the projectile may be inserted from the mouth to the base of the tube and seated securely adjacent the propellant charge with relative ease. The gap, called windage
Windage is a term used in aerodynamics, firearms ballistics, and automobiles.
Usage
Aerodynamics
Windage is a force created on an object by friction when there is relative movement between air and the object. Windage loss is the reduction in e ...
, increases the size of the bore with respect to the diameter of the shot somewhere between 10% and 20% depending upon the year the tube was cast and the foundry
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals pr ...
responsible.
The relationship between bore diameter and projectile weight was severed following the widespread adoption of rifled weapons during the latter part of the 19th century. Guns continued to be classed by projectile weight into the mid-20th century, particularly in British service with guns such as the 2, 6 and 17 pounder anti-tank weapons
Anti-tank warfare originated from the need to develop technology and tactics to destroy tanks during World War I. Since the Triple Entente deployed the first tanks in 1916, the German Empire developed the first anti-tank weapons. The first deve ...
. However, this value no longer definitively related to bore diameter, since projectiles were no longer simple spheres—and in any case were more often hollow shells filled with explosives rather than solid iron shot.
See also
* List of cartridges by caliber
Calibers in the size range of (mm, inches):
* 2 mm (.079+ caliber)
* 3 mm (.118+ caliber)
* 4 mm (.157+ caliber)
* 5 mm (.197+ caliber)
* 6 mm (.236+ caliber)
* 7 mm (.276+ caliber)
* 8 mm (.315+ caliber)
*9 mm (.354+ caliber)
* 10 mm (.394+ ca ...
* List of handgun cartridges
List of handgun cartridges, approximately in order of increasing caliber.
Table of handgun cartridges
{, class="wikitable sortable" style="text-align:left"
, -
! Cartridge name , , Bulletdiameter , , Caselength , , Cartridgelength , , Type , ...
* List of rifle cartridges
List of rifle cartridges, by primer type, calibre and name.
File:Cartridge Sample 2.jpg, 350px, From left to right: 1 .17 HM2,2 .17 HMR, 2.5 .17 wsm, 3 .22LR, 4 .22 WMR, 5 .17/23 SMc, 6 5mm/35 SMc, 7 .22 Hornet, 8 .223 Remington, 9 .223 WSSM ...
* List of the largest cannons by caliber
The list of cannon by caliber contains all types of cannon through the ages listed in decreasing caliber size. For the purpose of this list, the development of large-calibre artillery can be divided into three periods, based on the kind of projec ...
* Table of handgun and rifle cartridges
This is a table of selected pistol/submachine gun and rifle/machine gun cartridges by common name. Data values are the highest found for the cartridge, and might not occur in the same load (e.g. the highest muzzle energy might not be in the same ...
Citations
External links
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