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Rifle cartridges: from left: 50 BMG * 300 Win Mag * 308 Winchester, 7.62 x 39 mm * 5.56 x 45 mm NATO * 22 LR Rifle cartridge comparison.jpg
Rifle cartridges: from left: 50 BMG300 Win Mag308 Winchester, 7.62 × 39 mm5.56 × 45 mm NATO22 LR
A 45 ACP hollowpoint (Federal HST) with two 22 LR cartridges for comparison 22-45.jpg
A 45 ACP hollowpoint (Federal HST) with two 22 LR cartridges for comparison
Side view of a Sellier & Bellot 45-cal ACP cartridge with a metric ruler for scale 45 ACP - FMJ - SB - 2.jpg
Side view of a Sellier & Bellot 45-cal ACP cartridge with a metric ruler for scale

In guns, particularly firearms, caliber (or calibre in British English; sometimes abbreviated as "cal") 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. [1] It is measured in inches or in millimeters. [2] In the United States it is expressed in hundredths of an inch; in Great Britain in thousandths; in Europe 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. Due to the fact that 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 barrel, the distance is measured between opposing lands or between opposing grooves; groove measurements are common in cartridge designations originating in the United States, while land measurements are more common elsewhere in the world. Measurements "across the grooves" are used for maximum precision because rifling 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.

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 rifle", which could accommodate any of a wide range of cartridges using a roughly 0.30 inches (7.6 mm) 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 firearms and projectiles are often "categorized"[ by whom? ] 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.

Calibers fall into four general categories by size:

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

Makers of early cartridge arms had to invent methods of naming cartridges since no established convention existed then. [3] One of the early established cartridge arms was the Spencer repeating rifle, which Union forces used in the American Civil War. It was named based on the chamber 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 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, 44-40, and 32-20 were designated by bullet diameter to hundredths of an inch and standard black powder charge in grains. Optionally, the bullet weight in grains was designated, e.g. 45-70-405. [2] This scheme was far more popular and was carried over after the advent of early smokeless powder cartridges such as the 30-30 Winchester and 22 Long. Later developments used terms to indicate relative power, such as .44 Special and .44 Magnum. Variations on these methods persist today, with new cartridges such as the 204 Ruger and 17 HMR (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. [2]

The means of measuring a rifled bore varies, and may refer to the diameter of the lands or the grooves of the rifling. [2] For example, the 257 Roberts and 250 Savage 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. [4] The .308 Winchester 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. [5]

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, they more often reach the end of their barrel life, whereby the rifling is worn down to a point where a rifle loses some of its accuracy, the choice to make a caliber or cartridge change is often done at the same time as when a new rifle barrel is fitted to the rifle by a gunsmith. 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 [6] 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 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".

Common calibers in inch and their metric equivalents [7] [8] [9] [10] [11]
CaliberMetric caliberTypical bullet diameterCommon cartridgesNotes
172 4 mm 0.172 in 17 HMR, 17 Hornet, 17 Ackley Hornet, 17 Winchester Super Magnum, 17-32 Magnum, 17 VHA, 17 Remington, 17/222, 17 Mach III-IV, 17 Ackley Improved Bee, 17-357 RG, 17 Remington Fireball, 17 Incinerator, 4.39×39R mm SPS
20, 204 5 mm 0.204 in 204 Ruger, 5mm Remington Rimfire Magnum
2215.45 mm0.221 in 5.45×39mm Russian familyRussian Mil Std
225.6 mm0.223 in 22 Short, 22 Long, 22 Long Rifle, 22 Stinger, 22 Extra Long, 22 WMR (magnum), 297/230 Morris Extra Long, 22 Hornet, 22 Rem Automatic, 5.66 x39 MPS, 22 Rem Jet
2245.7 mm0.224 in 218 Bee, 219 Zipper, 22 Hornet-K, 220 Swift, 222 Remington, 222 Remington Magnum, 223 Remington, 5.56×45 mm NATO, 5.7×28 mm, .22 TCM, 5.8 × 42 Chinese, 224 Weatherby Magnum, 225 Winchester, 223 Winchester Super Short Magnum (Obsolete) 223 Ackley Improved, 219 Donaldson Wasp, 221 Remington Fireball, 22-250 Remington and many more
243 6 mm 0.243 in 243 Winchester, 244 Remington, 6 mm Remington, 6 mm Whisper, 6 mm PPC, 6 mm Bench Rest Remington, 6 × 45 mm, 6 × 47 mm, 6 mm Cheetah, 240 Weatherby, 6 × 62 Freres, 6 mm Norma BR, 6 X C Tubb, 6 mm JDJ, 6 mm SAW, 6-250 Walker, 6.17 Spitfire, 6.17 Flash, 6 mm Lee Navy, and more,
256.35 mm0.257 in, 6.35 mm 25 ACP (0.251"), 250/3000 Savage, 257 Roberts, 25-06 (0.257"),also called .25 Auto and 6.35mm Browning
266.5 mm0.264 in, 6.7 mm 6.5 × 55 mm Swedish, 260 Remington, 26 Nosler, 6.5 mm Creedmoor, 6.5×47 mm Lapua, 6.5 mm Grendel cartridges commonly known as '6.5 mm'
276.8 mm0.277 in, 7.035 mm 270 Winchester, 6.8 SPC
284 7 mm 0.284 in, 7.213 mm 280 Remington, 7 mm-08 Remington, 7 mm Weatherby Magnum, 7 mm Remington Magnum, 7 × 57 mm Mauser, 7 × 64 mm commonly called '7 mm'
3087.62 mm0.308 in, 7.82 mm30 Luger (7.65 × 21 mm Luger), 30-30 Win, 30 Herrett, 300 Whisper, 30-378 Weatherby, 7.63 Mannlicher–Schoenauer, 7.63 Mauser, 30 USA Rimless, 308 Corbon, .3-9 Savage, 30 Kurz, 300 BLK (7.62 × 35 mm), 7.5mm Schmidt–Rubin, 300 Winchester Magnum, 30 Carbine, 309 JDJ, .30-03, .30-06 Springfield, .30-06 JDJ, .307 GNR, 308 Winchester (7.62 × 51 mm NATO), 300 Weatherby Magnum, 30 Army (30-40 Krag), 7.82 mm Lazzeroni, and dozens more
3117.9 mm0.311 in, 7.92 mm 303 British, 7.62 × 39 mm Soviet, 7.62 × 54 mmR, 7.62 × 25 mm, 7.7 × 58 mm 7.62×54mmR is actually 7.92 mm (Mosin, SVD, PKM, etc.) The same applies to 7.62×39mm (AK-47, AKM, etc.)
3127.94 mm0.312 in, 7.94 mm 32 ACP Also known as 7.65 × 17 mm Browning
323 8 mm 0.323 in, 8.20 mm 8×57 mm IS, 325 WSM, 8 mm Remington Magnum, 8 mm plastic (airsoft) BBs.32 caliber rifle cartridges
3388.6 mm0.338 in 338 Lapua Magnum, 338 Norma Magnum, 338 Winchester Magnum, 338-378 Weatherby Magnum C14 Timberwolf (Canadian Forces)
3559 mm0.355 in 9 mm Luger, 9×19 mm Parabellum, 9 mm Ultra, 9 mm Bayard Long, 9 mm Browning Long, 9 mm Mauser, 9 mm Winchester Magnum, 9 mm Glisenti, 9 × 21 mm, 9 × 23 mm Winchester, 9 mm Mi-Bullet, 9 mm Steyr, .356 Team Smith & Wesson, 9 mm Federal, 9 mm × 25 mm Dillon, 9mm Action Express, 357 SIG.
3569 mm0.356 in .380 ACP (9mm Short), 9×56mm Mannlicher–Schoenauer, 9mm × 57mm Mauser
357 9 mm 0.357 in 38 Super, 38 Special, 357 Magnum, 35 Remington Handgun cartridges known as "38" are .357 caliber. Generally .357 for revolvers and rifles, .355 in autoloaders
3639 mm0.363 in 9 × 18 mm Makarov
3659.3 mm0.365 in 9.3 × 62 mm, 9.3 × 64 mm Brenneke, 9.3 × 72 mmR, 9.3 × 74 mmR
3759.5 mm0.375 in, 9.53 mm 375 H&H Magnum, 9.5 × 57 mm Mannlicher–Schönauer (375 Rimless Nitro Express (RNE) × 2¼)
40 10 mm 0.400 in 40 S&W, 10 mm Auto
4410.9 mm0.429 in 444 Marlin, 4 S&W Russian, 44 S&W Special, 44 Remington Magnum, 44 Auto Mag, 440 Cor-Bon, 44/454 JDJ Woodswalker
4511.43 mm0.451–0.454 in 45 ACP, 45 GAP, 454 Casull, 45 Long Colt, 455 Webley, 45 Schofield, 460 S&W Magnum Bullet diameter depends on bullet type/material. Generally 0.451 in for full metal jacket bullets and 0.454 in for lead bullets.
5012.7 mm0.510 in, 12.95 mm 50 BMG, 50 Action Express, 12.7×108mm, 500 S&W Magnum, 50 Beowulf M2 Browning machine gun and other heavy machine guns, long-range rifles typified by Barrett products. Desert Eagle handgun.


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. [12] 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 [10.4 mm]), [12] 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).

Caliber as measurement of length

The length of artillery barrels has often been described in terms of multiples of the bore diameter e.g. a 4-inch gun of 50 calibers would have a barrel 4 in × 50 = 200 in long. A 50 caliber 16 inch gun (16 inch diameter shell), has a barrel length (muzzle to breech) 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 1,900 to 2,700 lb (860 to 1,220 kg) 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).[ citation needed ]

Pounds as a measure of cannon bore

Smoothbore cannon and carronade 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 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, until 1812, had a mass of 489.5 g whilst the contemporary English (avoirdupois) pound massed approximately 454 g. Thus, a French 32-pdr at the Battle of Trafalgar threw a shot with 1.138 kg (2.51 lb) 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, 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 responsible.

English gun classes c. 1800[ citation needed ]
gun class (pdr.)projectile mass (kg)shot diameter (cm)shot volume (cm3)approx. service bore (cm)

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. 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


  1. Brown, Edmund G. (2009). Handgun Safety Certificate. West Sacramento, California: California Department of Justice. p. 52.
  2. 1 2 3 4 Barnes, Frank C. (2016). Woodard, W. Todd (ed.). Cartridges of the World: A Complete and Illustrated Reference for More than 1500 Cartridges (15th ed.). Iola, Wis.: Krause Publications. p. 9. ISBN   978-1440246425. OCLC   934886116.
  3. Barnes, Frank C. (1997) [1965]. McPherson, M. L. (ed.). Cartridges of the World (8th ed.). DBI Books. pp.  8–12. ISBN   0-87349-178-5.
  4. Van Zwoll, Wayne (2011). Shooter's bible guide to rifle ballistics. Skyhorse Publishing. p. 18. ISBN   978-1-61608-224-6.
  5. Barnes, Frank C. (2016). Woodard, W. Todd (ed.). Cartridges of the World: A Complete and Illustrated Reference for More than 1500 Cartridges (15th ed.). Iola, Wis.: Krause Publications. p. 670. ISBN   978-1440246425. OCLC   934886116.
  6. "Bolt Face Database". 2020. Retrieved 2020-09-22.
  7. Accurate (2000). Accurate Smokeless Powders Loading Guide (Number Two (Revised) ed.). Prescott, AZ: Wolfe Publishing. p. 392. barcode 94794 00200.
  8. "Pistol and Rifle Lead Bullets".
  9. "Rifle Bullets".
  10. "LeadSafe Total Copper Jacket ("TCJ") Bullet List". Archived from the original on 1999-02-18. Retrieved 2007-12-05.
  11. Frank C Barnes. Cartridges of the World (14th ed.). Gun Digest Books.
  12. 1 2 Barnes, Frank C. (2016). Woodard, W. Todd (ed.). Cartridges of the World: A Complete and Illustrated Reference for More than 1500 Cartridges (15th ed.). Iola, Wis.: Krause Publications. p. 629. ISBN   978-1440246425. OCLC   934886116.

Related Research Articles

A rifle is a long-barrelled firearm designed for accurate shooting, with a barrel that has a helical pattern of grooves (rifling) cut into the bore wall. In keeping with their focus on accuracy, rifles are typically designed to be held with both hands and braced firmly against the shooter's shoulder via a buttstock for stability during shooting. Rifles are used extensively in warfare, self defense, law enforcement, hunting, and shooting sports.

Shotgun Firearm intended for firing a bolus of small pellets

A shotgun is a long-barreled firearm designed to shoot a straight-walled cartridge known as a shotshell, which usually discharges numerous small pellet-like spherical sub-projectiles called shot, or sometimes a single solid projectile called a slug. Shotguns are most commonly smoothbore firearms, meaning that their gun barrels have no rifling on the inner wall, but rifled barrels for shooting slugs are also available.

Cartridge (firearms) Ammunition consisting of a casing, projectile, propellant and primer

A cartridge or a round is a type of pre-assembled firearm ammunition packaging a projectile, a propellant substance and an ignition device (primer) within a metallic, paper, or plastic case that is precisely made to fit within the barrel chamber of a breechloading gun, for the practical purpose of convenient transportation and handling during shooting. Although in popular usage the term "bullet" is often informally used to refer to a complete cartridge, it is correctly used only to refer to the projectile.

Rifling Gunsmithing technique

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 projectile longitudinally by conservation of angular momentum, improving its aerodynamic stability and accuracy over smoothbore designs.

Rimfire ammunition

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.

Gun barrel Firearm component which guides the projectile during acceleration

A gun barrel is a crucial part of gun-type ranged 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 gas(es) is used to propel a projectile out of the front end (muzzle) at a high velocity. The hollow interior of the barrel is called the bore, and the diameter of the bore is called its caliber, usually measured in inches or millimetres.

.22 Long Rifle

The .22 Long Rifle or simply .22 LR 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.

Internal ballistics, a subfield of ballistics, is the study of the propulsion of a projectile.

Shotgun shell Self-contained cartridge loaded with lead shot or a solid slug

A shotgun shell, shotshell or simply shell is a type of rimmed, cylindrical (straight-walled) cartridges used specifically by shotguns, and is typically loaded with numerous small, pellet-like spherical sub-projectiles called shot, fired through a smoothbore barrel with a tapered constriction at the muzzle to regulate the extent of scattering. A shell can sometimes also contain only a single large solid projectile known as a slug, fired usually through a rifled slug barrel. The shell casing usually consist of a paper or plastic tube mounted on a brass base holding a primer, and the shots are typically contained by a wadding/sabot inside the case. The caliber of the shotshell is known as its gauge.

.410 bore

The .410 bore is one of the smallest caliber of shotgun shell commonly available. A .410 bore shotgun loaded with shot shells is well suited for small game hunting and pest control. The .410 started off in the UK as a garden gun along with the .360 and the Nos. 3, 2 and 1 bore rimfires. .410 shells have similar base dimensions to the .45 Colt cartridge, allowing many single-shot firearms, as well as some derringers chambered in that caliber, to fire .410 shot shells without any modifications.

Shotgun slug Type of ammunition used mainly in hunting game

A modern shotgun slug is a heavy projectile made of lead, copper, or other material and fired from a shotgun. Slugs are designed for hunting large game, self-defense, and other uses. The first effective modern shotgun slug was introduced by Wilhelm Brenneke in 1898, and his design remains in use today. Most shotgun slugs are designed to be fired through a cylinder bore or an improved cylinder choke, rifled choke tubes, or fully rifled bores. Slugs differ from round-ball lead projectiles in that they are stabilized in some manner.

Gauge (firearms) Bore diameter

The gauge of a firearm is a unit of measurement used to express the inner diameter of the barrel.

Express (weaponry)

The term express was first applied to hunting rifles and ammunition beginning in the middle 19th century, to indicate a rifle or ammunition capable of higher than typical velocities. The early express cartridges used a heavy charge of black powder to propel a lightweight, often hollow point bullet, at high velocities to maximize point blank range. Later the express cartridges were loaded with nitrocellulose based gunpowder, leading to the Nitro Express cartridges, the first of which was the .450 Nitro Express.

.45-70 Rifle cartridge designed by the United States Government

The .45-70 rifle cartridge, also known as .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 replacement for the stop-gap .50-70 Government cartridge, which had been adopted in 1866, one year after the end of the American Civil War.

Caliber conversion sleeve

A caliber conversion sleeve or adapter sleeve is a device which can be used to non-permanently alter a firearm to allow it to fire a different cartridge than the one it was originally designed to fire. The different cartridge must be smaller in some dimensions than the original design cartridge. Alternative names sometimes imply the type of dimensional difference. A chamber insert may be used for a shorter cartridge of similar base diameter. A supplemental chamber or cartridge adapter is typically used for a shorter cartridge of reduced diameter. A cartridge conversion sleeve may include a short barrel of reduced bore diameter. Shotgun conversion sleeves may be called subgauge inserts, subgauge tubes, or gauge reducers. Sleeves intended for rifle or handgun cartridges may have rifled barrels. Additional variations may allow centerfire weapons to fire rimfire ammunition and/or retain autoloading function with the smaller cartridge.

The following are terms related to firearms and ammunition topics.

The 8 bore, also known as the 8 gauge, is an obsolete caliber used commonly in the 19th-century black-powder firearms.

4 bore

Four bore or 4 bore is an almost obsolete black powder caliber of the 19th century, used for the hunting of large and potentially dangerous game animals. The specifications place this caliber between the larger two bore and the lesser six bore. This caliber was the quintessential elephant gun caliber of the black powder safari rifles. The caliber was also used for the Coffman cartridges used for starting large aero engines such as the Rolls-Royce Griffon as used in the later Marks of Supermarine Spitfire.

The 6 bore, also known as the 6 gauge, is an obsolete caliber that was used commonly in 19th-century black-powder firearms.

.500 S&W Magnum

The .500 S&W Magnum (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. It has two primary design purposes: as a hunting handgun cartridge capable of taking all North American game species, and to be the most powerful production handgun cartridge to date. To put the cartridge’s extreme level of power into perspective; the muzzle energy of a .500 S&W bullet fired from a typical commercial loading of the round is roughly equivalent to that of a 16 pound bowling ball traveling at a speed of over 70 mph.