A cartridge is a type of pre-assembled firearm ammunition packaging a projectile, a propellant substance and an ignition device within a metallic, paper or plastic case, 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 used to refer to a complete cartridge, it is used only to refer to the projectile. Cartridges can be categorized by the type of their primers — a small charge of an impact- or electric-sensitive chemical mixture, located at the center of the case head, inside the rim of the case base, in a sideway projection, shaped like a pin or a lip, or in a small nipple-like bulge at the case base. Military and commercial producers continue to pursue the goal of caseless ammunition; some artillery ammunition uses the same cartridge concept. In other cases, the artillery shell is separate from the propellant charge. A cartridge without a projectile is called a blank.
One, inert is called a dummy. One that failed to ignite and shoot off the projectile is called a dud, one that ignited but failed to sufficiently push the projectile out of the barrel is called a squib; the primary purpose is to be a handy all-in-one for a shot. In modern, automatic weapons, it provides the energy to move the parts of the gun which make it fire repeatedly. Many weapons were designed to make use of a available cartridge, or a new one with new qualities; the cartridge case seals a firing chamber in all directions excepting the bore. A firing pin ignites it; the primer compound deflagrates, it does not detonate. A jet of burning gas from the primer ignites the propellant. Gases from the burning powder expand the case to seal it against the chamber wall; these propellant gases push on the bullet base. In response to this pressure, the bullet will move in the path of least resistance, down the bore of the barrel. After the bullet leaves the barrel, the chamber pressure drops to atmospheric pressure.
The case, elastically expanded by chamber pressure, contracts slightly. This eases removal of the case from the chamber. To manufacture brass for cartidges, a sheet of brass is punched into disks; these disks go through a series of punches and dies and are annealed and washed before moving to the next series of dies. Making bullets involves simular type of maching as for making brass cases; the projectile can be made of anything. Lead is a material of choice because of high density, ductility; the propellant was long gunpowder, still in use, but superseded by better compositions, generically called Smokeless powder. Early primer was fine gunpowder poured into a pan or tube where it could be ignited by some external source of ignition such as a fuse or a spark. Modern primers are shock sensitive chemicals enclosed in a small capsule, ignited by percussion. In some instance ignition is electricity-primed, there may be no primer at all in such design; the case is made of brass because it is resistant to corrosion.
A brass case head can be work-hardened to withstand the high pressures of cartridges, allow for manipulation via extraction and ejection without tearing the metal. The neck and body portion of a brass case is annealed to make the case ductile enough to allow reforming so that it can be reloaded many times. Steel is used in some plinking ammunition, as well as in some military ammunition. Steel is less expensive than brass. Military forces consider small arms cartridge cases to be disposable, one-time-use devices. However, case weight affects how much ammunition a soldier can carry, so the lighter steel cases do have a military advantage. Conversely, steel is more susceptible to contamination and damage so all such cases are varnished or otherwise sealed against the elements. One downside caused by the increased strength of steel in the neck of these cases is that propellant gas can blow back past the neck and into the chamber. Constituents of these gases condense on the chamber wall; this solid propellant residue can make extraction of fired cases difficult.
This is less of a problem for small arms of the former Warsaw Pact nations, which were designed with much larger chamber tolerances than NATO weapons. Aluminum cased; these are not reloaded as aluminum fatigues during firing and resizing. Some calibers have non-standard primer sizes to discourage reloaders from attempting to reuse these cases. Plastic cases are used in shotgun shells and some manufacturers offer polymer centerfire cartridges. Paper had been used in the earliest cartridges. Critical cartridge specifications include neck size, bullet weight and caliber, maximum pressure, overall length, case body diameter and taper, shoulder design, rim type, etc. Ever
A wildcat cartridge shortened to wildcat, is a custom cartridge for which ammunition and/or firearms are not mass-produced. These cartridges are created in order to optimize a certain performance characteristic of an existing commercial cartridge. Developing and using wildcat cartridges does not serve a purpose in military or law enforcement. There are endless varieties of wildcat cartridge: one source of gunsmithing equipment has a library of over 6,000 different wildcat cartridges for which they produce equipment such as chamber reamers. Wildcats are commercially sold rounds that have been modified in some way to alter the cartridge's performance. Barrels for the caliber are manufactured by gunsmiths specializing in barrel making; the same makers offer reloading dies, tools to custom-load bullets into cases. Because changing the barrel of a gun to accommodate custom cartridges requires precision equipment, most wildcats are developed by or in association with custom barrel makers. Ammunition is handloaded, using modified parent cases and the gunsmith-provided wildcat dies.
The supplier of the barrel or dies will provide the buyer with basic reloading data, giving a variety of powders, charge weights, bullet weights that can be used for developing loads. Handloaders use the data to develop a load by starting with minimum loads and working up. Wildcat cases and cartridges can be found for sale, but only from small makers. Larger manufacturers do not produce wildcats because there is such a limited market for them and because there are no established CIP or SAAMI standards, which causes liability concerns. Wildcat cartridges are developed for many reasons; the goal is to optimize some characteristic of a commercial cartridge in a given context. Higher velocities, greater energy, better efficiency, greater consistency and complying to a minimal permitted caliber or bullet weight for the legal hunting of certain species of game in a particular jurisdiction are the top reasons; the sport of metallic silhouette shooting, has given rise to a great number of wildcats, as several rifle rounds are adapted to fire from a handgun.
In using autopistols for hunting or competitive shooting, improved feeding of softnose or hollowpoint bullets is an issue. Wildcat cartridges are developed because: Higher velocities can be obtained by increasing the case capacity, or reducing the caliber. Greater energy can be attained by increasing the case capacity. Better efficiency can be achieved by increasing the shoulder angle, shortening the case, reducing case taper. Greater consistency can be achieved by tuning the case capacity to a certain bullet diameter and velocity that give consistent results. Feeding problems can be fixed; some methods used to develop a wildcat are: Cold forming. The parent case is well lubricated and forced into the reloading die for the wildcat caliber; this will swage the case into the new shape. This type of operation is used for reducing case dimensions, such as changing the neck diameter or pushing the shoulder back. Fire forming; this consists of taking the parent case, or a cold formed case, loading it with a light bullet and light load of powder, firing it in the firearm it will be used in.
Another technique uses a charge of fast burning powder topped with a case full of Cream of Wheat and a wad, to form a special blank cartridge that will expand the case. This technique is used for increasing case dimensions, such as pushing the neck forward, increasing the neck angle, or straightening the case walls. Trimming to length. After either a cold forming or a fire forming operation, the mouth of the case will be longer than ideal, the case will be trimmed back to the "trim to" length. Trimming is a normal reloading operation, as high pressure cartridges will flow each time they are fired, periodically need trimming to remove the brass that flows to the mouth. Changing the diameter of the case. Called "necking up" or "necking down", this is the most common way of making a wildcat; the new caliber allows a much different range of bullet weights, can increase the velocity or the power or the resistance to wind drift as compared to the parent cartridge. Necking back; this is a cold forming operation.
This is done when developing rounds for shorter barrels, such as turning a rifle cartridge into a handgun cartridge. Blowing out; this is a fire forming operation. Changing the shoulder angle. By making the shoulder closer to square, the resulting space is closer to the ideal spherical shape, resulting in a more efficient burn. If the shoulder is to be moved back, this is a cold forming operation. Reducing the case taper; this hot forming operation makes the cartridge more cylindrical, giving similar results to a shoulder angle change. Changing the rim. While this is a wildcatting operation, it is only done by commercial operations, due to the precision turning needed; this is a conversion from rimmed to rimless cartridge, or from rimless to rebated, is
A rifle is a portable, long-barrelled firearm designed for long-range precision shooting, to be held with both hands and braced against the shoulder for stability during firing, with a barrel that has a helical pattern of grooves cut into the bore walls. The term was rifled gun, with the word "rifle" referring to the machining process of creating grooving with cutting tools, is now used for any long handheld device designed for aimed discharge activated by a trigger, such as air rifles and the personnel halting and stimulation response rifle. Rifles are used in warfare, law enforcement and shooting sports. Like all typical firearms, a rifle's projectile is propelled by the contained deflagration of a combustible propellant compound, although other means such as compressed air are used in air rifles, which are popular for vermin control, hunting small game, formal target shooting and casual shooting; the raised areas of the rifling are called "lands," which make contact with the projectile, imparting a spin around the longitudinal axis of the barrel.
When the projectile leaves the barrel, this spin lends gyroscopic stability to the projectile and prevents tumbling, in the same way that a properly spirally thrown American football or rugby ball behaves. This thus improves range and accuracy. Rifles only fired a single projectile with each squeeze of the trigger. Modern rifles are classified as single shot, bolt action, semi-automatic, or automatic. Single shot, bolt action, semi-automatic rifles are limited by their designs to fire a single shot for each trigger pull. Only automatic rifles are capable of firing more than one round per trigger squeeze. Modern automatic rifles overlap to some extent in function with machine guns. In fact, many light machine guns are adaptations of existing automatic rifle designs. A military's light machine guns are chambered for the same caliber ammunition as its service rifles; the difference between an automatic rifle and a machine gun comes down to weight, cooling system, ammunition feed system. Rifles, with their lighter components and smaller capacity magazines, are incapable of sustained automatic fire in the way that machine guns are.
Modern military rifles are fed by magazines, while machine guns are belt-fed. Many machine guns allow the operator to exchange barrels in order to prevent overheating, whereas rifles do not. Most machine guns fire from an open bolt in order to reduce the danger of "cook-off", while all rifles fire from a closed bolt for accuracy. Machine guns are crewed by more than one soldier; the term "rifle" is sometimes used to describe larger rifled crew-served weapons firing explosive shells, for example, recoilless rifles and naval rifles. In many works of fiction a rifle refers to any weapon that has a stock and is shouldered before firing if the weapon is not rifled or does not fire solid projectiles; the origins of rifling are difficult to trace, but some of the earliest practical experiments seem to have occurred in Europe during the 15th century. Archers had long realized that a twist added to the tail feathers of their arrows gave them greater accuracy. Early muskets produced large quantities of smoke and soot, which had to be cleaned from the action and bore of the musket either through the action of repeated bore scrubbing, or a deliberate attempt to create "soot grooves" that would allow for more shots to be fired from the firearm.
This might have led to a perceived increase in accuracy, although no one knows for sure. True rifling dates from the mid-15th century, although military commanders preferred smooth bore weapons for infantry use because rifles were much more prone to problems due to powder fouling the barrel and because they took longer to reload and fire than muskets. Rifles were created as an improvement in the accuracy of smooth bore muskets. In the early 18th century, Benjamin Robins, an English mathematician, realized that an elongated bullet would retain the momentum and kinetic energy of a musket ball, but would slice through the air with greater ease; the black powder used in early muzzle-loading rifles fouled the barrel, making loading slower and more difficult. Their greater range was considered to be of little practical use, since the smoke from black powder obscured the battlefield and made it impossible to target the enemy from a distance. Since musketeers could not afford to take the time to stop and clean their barrels in the middle of a battle, rifles were limited to use by sharpshooters and non-military uses like hunting.
Muskets were smoothbore, large caliber weapons using ball-shaped ammunition fired at low velocity. Due to the high cost and great difficulty of precision manufacturing, the need to load from the muzzle, the musket ball was a loose fit in the barrel. On firing the ball bounced off the sides of the barrel when fired and the final direction on leaving the muzzle was unpredictable; the performance of early muskets defined the style of warfare at the time. Due to the lack of accuracy, soldiers were deployed in long lines to fire at the opposing forces. Precise aim was thus not necessary to hit an opponent. Muskets were used for comparatively rapid, imprecise
A proof test is a form of stress test to demonstrate the fitness of a load-bearing structure. An individual proof test may apply only to the unit tested, or to its design in general for mass-produced items; such a structure is subjected to loads above that expected in actual use, demonstrating safety and design margin. Proof testing is nominally a nondestructive test if both design margins and test levels are well-chosen. However, unit failures are by definition considered to have been destroyed for their originally-intended use and load levels. Proof tests may be performed before a new design or unit is allowed to enter service, or perform additional uses, or to verify that an existing unit is still functional as intended. Cranes and derricks are proof tested when called on for dangerous load levels or high-valued cargoes. Items which are smaller and more common are in the load path and a failure risk if not tested. Testing involves lifting weight or drawing tension equal to or greater than design levels.
An overspeed proof test involves physically running the machine at high speed up to the test speed. This may be done during manufacture as an initial proof test. Physical overspeed tests may be periodically undertaken on some machines to verify operation of the overspeed protection systems. Operation at speeds above the normal operating speed can increase stress levels in rotating parts. Failing flywheels, etc. may present a shrapnel risk in case of a failure. Swords would be proof tested by impact before issuance- the "British test". Vessels which may be a failure risk, such as utility-scale water towers, chemical-handling equipment, or very-high-pressure storage tanks, may be proof tested. Rocket stage tankage, being high-valued and the vehicle's primary structure, are proof-tested when redesigned, may be tested at the unit level. Testing involves exposure to higher gauge pressures than design levels, or in some cases, pulling harder vacuum. A firearm's chamber and barrel become pressure vessels for brief periods.
In firearm terminology, a proof test is a test wherein a deliberately over-pressured round is fired from a firearm in order to verify that the firearm is not defective and will not explode on firing. The firearm is inspected after the test, if it is found to be in sound condition it is marked with a "proof mark" to indicate that it has been proofed. In many jurisdictions a proof test and valid proof mark are required for the sale of firearms. A "proof round" is an ammunition assembly designed to be used in proof testing. A "proof shot" is a special projectile used in a proof round or other projectile weapons, electromagnetic guns for example. Small arms proof rounds resemble normal cartridges, though they will bear special markings to prevent them from being confused for standard cartridges. Large calibre arms, such as artillery, will in general use an inert solid projectile. For both small arms and heavy weapons, the gun is fired remotely and examined. In the case of revolvers or other multi-chamber firearms, each chamber must be proof tested before the firearm may be marked.
Examination of the firearm may be as simple as visually inspecting it or may involve more in-depth examination, at the option of the tester. Because proof testing may or may not result in the destruction of the test specimen, it falls on the border between destructive testing and nondestructive testing. A proof mark is a mark specific to the manufacturer, importer, or testing facility, performing the test, it takes the form of a stamp that makes an impression in the metal. Since proof marks are unique and nearly universal, they are used to identify the origins of firearms that lack normal manufacturer's markings, such as military weapons, which are produced by large numbers of different manufacturers. A small arms proof round is loaded to a higher than normal service pressure, stressing both the gun barrel and breech during firing; this can be due to a heavy projectile fired using the standard propelling charge, the standard projectile fired with a different propellant type or weight, or combinations of charge and bullet weight to give the required proofing pressure.
Minimum proof testing pressures are specified by the owner of the cartridge specification, such as C. I. P. or SAAMI for most commercial cartridges or NATO EPVAT testing for appropriate military cartridges. An example proofing round for the.50 BMG is the "Cartridge, Caliber.50, High Pressure, M1". This uses the standard weight.50 BMG M1 round propellant. The M1 proof round gives a proofing pressure of ~65,000 psi, 11,000 psi above the standard service pressure. In C. I. P. member states every civil firearm has to be professionally proofed in accredited Proof Houses before it can be sold to consumers. The proofsigns can allow to identify special periods of times; some of the acctually used signs are: Proofhouse Cologne since 1991 german final proofmark for test with nitropropellant: Proofhouse Ferlach Proofhouse Vienna Proofhouse Abu Dhabi The standard proof test consist of firing two overloaded cartridges that produce 25% more chamber pressure than the C. I. P. Specified maximum pressure l
Czechoslovakia, or Czecho-Slovakia, was a sovereign state in Central Europe that existed from October 1918, when it declared its independence from the Austro-Hungarian Empire, until its peaceful dissolution into the Czech Republic and Slovakia on 1 January 1993. From 1939 to 1945, following its forced division and partial incorporation into Nazi Germany, the state did not de facto exist but its government-in-exile continued to operate. From 1948 to 1990, Czechoslovakia was part of the Eastern Bloc with a command economy, its economic status was formalized in membership of Comecon from 1949 and its defense status in the Warsaw Pact of May 1955. A period of political liberalization in 1968, known as the Prague Spring, was forcibly ended when the Soviet Union, assisted by several other Warsaw Pact countries, invaded. In 1989, as Marxist–Leninist governments and communism were ending all over Europe, Czechoslovaks peacefully deposed their government in the Velvet Revolution. In 1993, Czechoslovakia split into the two sovereign states of Slovakia.
Form of state1918 – 1938: A democratic republic championed by Tomáš Masaryk. 1938 – 1939: After annexation of Sudetenland by Nazi Germany in 1938, the region turned into a state with loosened connections among the Czech and Ruthenian parts. A large strip of southern Slovakia and Carpatho-Ukraine was annexed by Hungary, the Zaolzie region was annexed by Poland. 1939 – 1945: The region was split into the Protectorate of Bohemia and Moravia and the Slovak Republic. A government-in-exile continued to exist in London, supported by the United Kingdom, United States and their Allies. Czechoslovakia adhered to the Declaration by United Nations and was a founding member of the United Nations. 1946 – 1948: The country was governed by a coalition government with communist ministers, including the prime minister and the minister of interior. Carpathian Ruthenia was ceded to the Soviet Union. 1948 – 1989: The country became a socialist state under Soviet domination with a centrally planned economy. In 1960, the country became a socialist republic, the Czechoslovak Socialist Republic.
It was a satellite state of the Soviet Union. 1969 – 1990: The federal republic consisted of the Czech Socialist Republic and the Slovak Socialist Republic. 1990 – 1992: Following the Velvet Revolution, the state was renamed the Czech and Slovak Federal Republic, consisting of the Czech Republic and the Slovak Republic, reverted to a democratic republic. NeighboursAustria 1918 – 1938, 1945 – 1992 Germany Hungary Poland Romania 1918 – 1938 Soviet Union 1945 – 1991 Ukraine 1991 – 1992 TopographyThe country was of irregular terrain; the western area was part of the north-central European uplands. The eastern region was composed of the northern reaches of the Carpathian Mountains and lands of the Danube River basin. ClimateThe weather is mild summers. Influenced by the Atlantic Ocean from the west, Baltic Sea from the north, Mediterranean Sea from the south. There is no continental weather. 1918–1920: Republic of Czechoslovakia /Czecho-Slovak State, or Czecho-Slovakia/Czechoslovakia 1920–1938: Czechoslovak Republic, or Czechoslovakia 1938–1939: Czecho-Slovak Republic, or Czecho-Slovakia 1945–1960: Czechoslovak Republic, or Czechoslovakia 1960–1990: Czechoslovak Socialist Republic, or Czechoslovakia April 1990: Czechoslovak Federative Republic and Czecho-Slovak Federative Republic The country subsequently became the Czech and Slovak Federative Republic, or Československo and Česko-Slovensko.
The area was long a part of the Austro-Hungarian Empire until the empire collapsed at the end of World War I. The new state was founded by Tomáš Garrigue Masaryk, who served as its first president from 14 November 1918 to 14 December 1935, he was succeeded by his close ally, Edvard Beneš. The roots of Czech nationalism go back to the 19th century, when philologists and educators, influenced by Romanticism, promoted the Czech language and pride in the Czech people. Nationalism became a mass movement in the second half of the 19th century. Taking advantage of the limited opportunities for participation in political life under Austrian rule, Czech leaders such as historian František Palacký founded many patriotic, self-help organizations which provided a chance for many of their compatriots to participate in communal life prior to independence. Palacký supported Austro-Slavism and worked for a reorganized and federal Austrian Empire, which would protect the Slavic speaking peoples of Central Europe against Russian and German threats.
An advocate of democratic reform and Czech autonomy within Austria-Hungary, Masaryk was elected twice to the Reichsrat, first from 1891 to 1893 for the Young Czech Party, again from 1907 to 1914 for the Czech Realist Party, which he had founded in 1889 with Karel Kramář and Josef Kaizl. During World War I small numbers of Czechs, the Czechoslovak Legions, fought with the Allies in France and Italy, while large numbers deserted to Russia in exchange for its support for the independence of Czechoslovakia from the Austrian Empire. With the outbreak of World War I, Masaryk began working for Czech independence in a union with Slovakia. With Edvard Beneš and Milan Rastislav Štefánik, Masaryk visited several Western countries and won support from influential publicists. Bohemia and Moravi
A machine gun is a automatic mounted or portable firearm designed to fire rifle cartridges in rapid succession from an ammunition belt or magazine for the purpose of suppressive fire. Not all automatic firearms are machine guns. Submachine guns, assault rifles, battle rifles, pistols or cannons may be capable of automatic fire, but are not designed for sustained fire; as a class of military rapid-fire guns, machine guns are automatic weapons designed to be used as support weapons and used when attached to a mount- or fired from the ground on a bipod or tripod. Many machine guns use belt feeding and open bolt operation, features not found on rifles. In the U. S. A, a "machine gun" is a legal term for any weapon able to fire more than one shot per function of the trigger regardless of caliber, the receiver of any such weapon, any weapon convertible to such a state using normal tools, or any component or part that will modify an existing firearm such that it functions as a "machine gun" such as a drop-in auto sear.
Civilian possession of such weapons manufactured prior to 1986 is not prohibited by any federal law and not illegal in many states, but they must be registered as Title II weapons under the National Firearms Act and have a tax stamp paid. Machine guns manufactured after 1986 are prohibited by the Hughes Amendment to the Gun Owners Protection Act. Unlike semi-automatic firearms, which require one trigger pull per round fired, a machine gun is designed to fire for as long as the trigger is held down. Nowadays the term is restricted to heavy weapons, able to provide continuous or frequent bursts of automatic fire for as long as ammunition lasts. Machine guns are used against personnel and light vehicles, or to provide suppressive fire, either directly or indirectly, they are mounted on fast attack vehicles such as technicals to provide heavy mobile firepower, armored vehicles such as tanks for engaging targets too small to justify use of the primary weaponry or too fast to engage with it, on aircraft as defensive armament or for strafing ground targets, though on fighter aircraft true machine guns have been supplanted by large-caliber rotary guns.
Some machine guns have in practice sustained fire continuously for hours. Because they become hot all machine guns fire from an open bolt, to permit air cooling from the breech between bursts, they usually have either a barrel cooling system, slow-heating heavyweight barrel, or removable barrels which allow a hot barrel to be replaced. Although subdivided into "light", "medium", "heavy" or "general-purpose" the lightest machine guns tend to be larger and heavier than standard infantry arms. Medium and heavy machine guns are either mounted on a vehicle. Light machine guns are designed to provide mobile fire support to a squad and are air-cooled weapons fitted with a box magazine or drum and a bipod. Medium machine guns use full-sized rifle rounds and are designed to be used from fixed positions mounted on a tripod. Heavy machine gun is a term originating in World War I to describe heavyweight medium machine guns and persisted into World War II with Japanese Hotchkiss M1914 clones. A general-purpose machine gun is a lightweight medium machine gun which can either be used with a bipod and drum in the light machine gun role or a tripod and belt feed in the medium machine gun role.
Machine guns have simple iron sights, though the use of optics is becoming more common. A common aiming system for direct fire is to alternate solid rounds and tracer ammunition rounds, so shooters can see the trajectory and "walk" the fire into the target, direct the fire of other soldiers. Many heavy machine guns, such as the Browning M2.50 caliber machine gun, are accurate enough to engage targets at great distances. During the Vietnam War, Carlos Hathcock set the record for a long-distance shot at 7,382 ft with a.50 caliber heavy machine gun he had equipped with a telescopic sight. This led to the introduction of.50 caliber anti-materiel sniper rifles, such as the Barrett M82. Other automatic weapons are subdivided into several categories based on the size of the bullet used, whether the cartridge is fired from a closed bolt or an open bolt, whether the action used is locked or is some form of blowback. Automatic firearms using pistol-calibre ammunition are called machine pistols or submachine guns on the basis of size.
The term personal defense weapon is sometimes applied to weapons firing dedicated armor-piercing rounds which would otherwise be regarded as machine pistols or SMGs, but it is not strongly defined and has been used to describe a range of weapons from ordinary SMGs to compact assault rifles. Selective fire rifles firing a full-power rifle cartridge from a closed bolt are called automatic rifles or battle rifles, while rifles that fire an intermediate cartridge are called assault rifles. Assault rifles are a compromise between the size and weight of a pistol-calibre submachine gun and a full size battle rifle, firing intermediate cartridges and allowing semi-automatic and burst or full-automatic fire options
In firearms, rifling is the helical groove pattern, machined into the internal 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. This spin serves to gyroscopically stabilize the projectile by conservation of angular momentum, improving its aerodynamic stability and accuracy over smoothbore designs. Rifling is described by its twist rate, which indicates the distance the rifling takes to complete one full revolution, such as "1 turn in 10 inches", or "1 turn in 254 mm". A shorter distance indicates a "faster" twist, meaning that for a given velocity the projectile will be rotating at a higher spin rate; the combination of length and shape of a projectile determines the twist rate needed to stabilize it – barrels intended for short, large-diameter projectiles like spherical lead balls require a low twist rate, such as 1 turn in 48 inches. Barrels intended for long, small-diameter bullets, such as the ultra-low-drag, 80-grain 0.223 inch bullets, use twist rates of 1 turn in 8 inches or faster.
In some cases, rifling will have twist rates that increase down the length of the barrel, called a gain twist or progressive twist. Long projectiles such as flechettes may require high twist rates. Muskets were smoothbore, large caliber weapons using ball-shaped ammunition fired at low velocity. Due to the high cost and great difficulty of precision manufacturing, the need to load and speedily from the muzzle, musket balls were a loose fit in the barrels. On firing the balls would bounce off the sides of the barrel when fired and the final destination after leaving the muzzle was less predictable; this was countered when accuracy was more important, for example when hunting, by using a tighter combination of a closer to bore sized ball and a patch. The accuracy was improved, but still not reliable for precision shooting over long distances. Barrel rifling was invented in Augsburg, Germany in 1498. In 1520 August Kotter, an armourer of Nuremberg, Germany improved upon this work. Though true rifling dates from the mid-16th century, it did not become commonplace until the nineteenth century.
The concept of stabilizing the flight of a projectile by spinning it was known in the days of bows and arrows, but early firearms using black powder had difficulty with rifling because of the fouling left behind by the combustion of the powder. The most successful weapons using rifling with black powder were breech loaders such as the Queen Anne pistol; the grooves most used in modern rifling have sharp edges. More polygonal rifling, a throwback to the earliest types of rifling, has become popular in handguns. Polygonal barrels tend to have longer service lives because the reduction of the sharp edges of the land reduces erosion of the barrel. Supporters of polygonal rifling claim higher velocities and greater accuracy. Polygonal rifling is seen on pistols from CZ, Heckler & Koch, Glock and Kahr Arms, as well as the Desert Eagle. For tanks and artillery pieces, the extended range, full bore concept developed by Gerald Bull for the GC-45 howitzer reverses the normal rifling idea by using a projectile with small fins that ride in the grooves, as opposed to using a projectile with a oversized driving band, forced into the grooves.
Such guns have achieved significant increases in muzzle range. Examples include the South African G5 and the German PzH 2000. Gain-twist rifling called progressive rifling, begins with little change in the projectile's angular momentum during the first few inches of bullet travel after ignition during the transition from chamber to throat; this enables the bullet to remain undisturbed and trued to the case mouth. After engaging the rifling the bullet is progressively subjected to accelerated angular momentum as burning powder propels it down the barrel. By only increasing the spin rate, torque is spread along a much longer section of barrel, rather than only at the throat where rifling is eroded through repeated rifling engagement. Gain-twist rifling was used as prior to and during the American Civil War. Colt Army and Navy revolvers both employed gain-twist rifling. Gain-twist rifling, however, is more difficult to produce than uniform rifling, therefore is more expensive; the military has used gain-twist rifling in a variety of weapons such as the 20 mm M61 Vulcan Gatling gun used in some current fighter jets and the larger 30 mm GAU-8 Avenger Gatling gun used in the A10 Thunderbolt II close air support jet.
In these applications it allows lighter construction of the barrels by decreasing chamber pressures through the use of low initial twist rates but ensuring the projectiles have sufficient stability once they leave the barrel. It is used in commercially available products, though notably on the Smith & Wesson Model 460. An early method of introducing rifling to a pre-drilled barrel was to use a cutter mounted on a square-section rod twisted into a spiral of the desired pitch, mounted in two fixed square-section holes; as the cutter was advanced through the barrel it twisted at a uniform rate governed by the pitch. The first cut was shallow but as repeated cuts were made the cutter points were expanded—the blades were in slots i