Caliber (artillery)

Rifled barrels introduce ambiguity to measurement of caliber. A rifled bore consists of alternating grooves and lands. The distance across the bore from groove to groove is greater than the distance from land to land. Projectiles fired from rifled barrels must be of the full groove-to-groove diameter to be effectively rotated by the rifling, but the caliber has sometimes been specified as the land-to-land diameter before rifling grooves were cut. The depth of rifling grooves (and the consequent ambiguity) increases in larger calibers.

Steel artillery projectiles may have a forward bourrelet section machined to a diameter slightly smaller than the original land-to-land dimension of the barrel and a copper driving band somewhat larger than the groove-to-groove diameter to effectively seal the bore as it becomes enlarged by erosion during prolonged firing.

United States Navy guns typically used rifling depth between one-half and one percent of caliber. Projectile bourrelet diameter specification was 0.015 inches (0.38 mm) less than land-to-land diameter with a minus manufacturing tolerance, so average clearance was about 0.012 inches (0.30 mm). Driving band diameter was groove-to-groove diameter plus 0.02 inches (0.51 mm).^[1]

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Rifling

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

Bourrelet

Bourrelet

A bourrelet is a portion of an elongated artillery projectile which is used in conjunction with the projectile's driving band, or rotating band, to stabilize its flight by keeping the fore part of the projectile precisely aligned with the barrel.

Copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.

Driving band

Driving band

A driving band or rotating band is a band of soft metal near the base of an artillery shell, often made of gilding metal, copper, or lead. When the shell is fired, the pressure of the propellant swages the metal into the rifling of the barrel and forms a seal; this seal prevents the gases from blowing past the shell, and engages the barrel's rifling to spin-stabilize the shell.

United States Navy

United States Navy

The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage of its active battle fleet alone exceeding the next 13 navies combined, including 11 allies or partner nations of the United States as of 2015. It has the highest combined battle fleet tonnage and the world's largest aircraft carrier fleet, with eleven in service, two new carriers under construction, and five other carriers planned. With 336,978 personnel on active duty and 101,583 in the Ready Reserve, the United States Navy is the third largest of the United States military service branches in terms of personnel. It has 290 deployable combat vessels and more than 2,623 operational aircraft as of June 2019.

The length of the barrel (especially for larger guns) is often quoted in multiples of the caliber, used, for example, in US Naval Rifles 3 in (76 mm) or larger.^[2] The effective length of the barrel (from breech to muzzle) is divided by the barrel diameter to give a dimensionless quantity.^[2]: 81 For example, the main guns of the Iowa-class battleships can be referred to as 16"/50 caliber. They are 16 inches in diameter and the barrel is 800 inches long (16 × 50 = 800). This is also sometimes indicated using the prefix L/; so for example, the most common gun for the Panzer V tank is described as a "75 mm L/70," meaning a barrel with an internal bore of 75 mm (3.0 in), and 5,250 mm (17 ft 3 in) long.

The bore to barrel length ratio is called "caliber" in naval gunnery,^[2]: 81 but is called "length" in army artillery. Before World War II, the US Navy used 5"/51 caliber (5" L/51) as surface-to-surface guns and 5"/25 caliber (5" L/25) as surface to air guns. By the end of World War II, the dual purpose 5-inch/38-caliber gun (5" L/38) was standard naval armament against surface and air targets. All three had a bore diameter of 5 inches (not 5.51 or 5.25 or 5.38 as often misread).

Naval rifles, although constructed and manufactured in roughly the same manners as land-based artillery, were built to much more stringent and studious standards than land-based weapons, and for good reason. At sea, a weapon had to perform, without fail. There was no ready replacement, nor one that could be readily supplied. Over time, the terms of pound (weight of shell) and bore (the actual bore of the weapon) became confused and blurred. Eventually, when the technology existed, the bore (in inches or millimetres) came to be the standard measure.^[3][4][5][6]

For naval rifles, the initial change was to actual bore, thus facilitating the manufacture of standard projectiles. They then began to measure the effective length (and therefore range) of the weapon in calibers. These are a measure of the standardized bore of the barrel versus the rifled bore of the barrel. In other words, a 12/45 is 12"×45= the length of the rifled bore of that gun in inches. This explains the differences in both penetration and long range performance of various naval rifles over the years.^[3][4][5][6]

In addition to the possible improvements in overall performance (i.e. muzzle velocity and striking force), the increase in barrel length also allowed, in some circumstances, an increase in projectile size as well. For example, the American 14/45, as introduced in the New York-class battleships, fired a 1,250 lb (570 kg) projectile. Later improvements to the design, lengthening the rifle itself and also altering the breech, allowed a 1400 lb. projectile and, overall, a greater barrel life. Again we see this pattern with the US 16" guns. The initial design was 45 calibers in length and fired a 2200 lb. shell. The later re-design to 50 calibre not only allowed a higher velocity but also a heavier 2700 lb. shell, which ultimately came to be accepted as the greatest naval shell ever deployed in combat.^[3][4][5][6]

Early gun barrels were short and thick, typically no more than 26 calibers, as the gunpowder propellant they used burned very quickly and violently, and hence its acceleration time was short. Slower-burning "brown powder" formulations of gunpowder allowed gun barrel length to increase slightly in the 1880s but enormous quantities of brown powder were required. New slower-burning "smokeless powder" propellants available from the 1880s onwards such as Poudre B, cordite and nitrocellulose allowed a gentler prolonged acceleration, hence gun barrels were made progressively longer and thinner. The new formulations were far more powerful propellants than gunpowder and far less was needed by weight as they transformed almost entirely to gases when burned. Muzzle velocity became limited only by the length of barrel that was feasible, both in terms of the construction methods of the day and in terms of any practical constraints imposed by the gun's manner of use.

The practical effect of long barrels for modern guns is that the projectile spends more time in the barrel before it exits, and hence more time is available for expanding gas from the controlled burning of the propellant charge to smoothly accelerate the projectile, bringing about a higher velocity without placing undue strain on the gun. In internal ballistics terms, if the base of a projectile is thought of as a piston propelled by the expanding gas, then as barrel length increases the volume swept by the piston also increases, and hence the amount of energy that can be extracted from the gas's burning increases. A longer barrel allows more propellant to be used: the propellant is all burned fairly early in the projectile's journey along the barrel, except in the very common instance where combustion is still occurring as the projectile leaves the muzzle and a visible muzzle "flash" is produced.

The projectile continues to accelerate as long as the pressure behind it is sufficient to overcome bore friction. The excess energy will continue to accelerate the projectile until it exits the muzzle. If the pressure behind the projectile drops sufficiently before the projectile leaves the bore, the projectile can and will slow while still within the barrel, despite residual bore pressure behind the projectile. A light charge with insufficient pressure to expel the projectile will result in a "squib", or projectile lodged in the bore. ^[7] This pressure is reduced by the increasing barrel volume the gas has to fill.

In order to achieve maximum muzzle velocity with the shortest barrel length, the projectile should exit the barrel as the gas pressure reduces to a small fraction of the maximum, although unlike chamber maximum chamber pressure, the small fraction desired is impossible to measure. In modern guns, increased muzzle velocities can be produced by altering powder composition and/or using duplex charges containing two different powders in order to extend the "pressure curve" farther down the bore. By exposing the projectile base to a given pressure for a longer length of time, velocity can be increased without elevating the pressure level generated.

Technological improvements had made it possible to introduce into use long gun barrels that are strong enough to withstand the forces involved in accelerating the shell to a high velocity, while remaining light enough to be reasonably mobile, rigid enough to maintain accuracy, and having a bore able to withstand many firings before needing refurbishment. In World War I 45-caliber naval gun barrels were typical, in World War II 50- to 55-caliber barrels were common, with Germany already manufacturing tank guns of 70 calibers by 1943.

Today, 60- to 70-caliber barrels are not uncommon, but the latest technology has allowed shorter barrels of 55 calibers to attain muzzle velocities of 1,750 m/s (5,700 ft/s), as with the Rheinmetall 120 mm tank gun. However, by using discarding sabots, many such guns fire projectiles which are much smaller than the gun bore, so the relationship of projectile size to barrel length is not as straightforward as with older ordnance.

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Iowa-class battleship

Iowa-class battleship

The Iowa class was a class of six fast battleships ordered by the United States Navy in 1939 and 1940. They were initially intended to intercept fast capital ships such as the Japanese Kongō class while also being capable of serving in a traditional battle line alongside slower battleships and act as its "fast wing". The Iowa class was designed to meet the Second London Naval Treaty's "escalator clause" limit of 45,000-long-ton (45,700 t) standard displacement. Four vessels, Iowa, New Jersey, Missouri, and Wisconsin, were completed; two more, Illinois and Kentucky, were laid down but canceled in 1945 and 1958, respectively, before completion, and both hulls were scrapped in 1958–1959.

5-inch/38-caliber gun

5-inch/38-caliber gun

The Mark 12 5"/38 caliber gun was a United States dual-purpose naval gun, but also installed in single-purpose mounts on a handful of ships. The 38 caliber barrel was a mid-length compromise between the previous United States standard 5"/51 low-angle gun and 5"/25 anti-aircraft gun. United States naval gun terminology indicates the gun fired a projectile 5 inches (127 mm) in diameter, and the barrel was 38 calibers long. The increased barrel length provided greatly improved performance in both anti-aircraft and anti-surface roles compared to the 5"/25 gun. However, except for the barrel length and the use of semi-fixed ammunition, the 5"/38 gun was derived from the 5"/25 gun. Both weapons had power ramming, which enabled rapid fire at high angles against aircraft. The 5"/38 entered service on USS Farragut, commissioned in 1934, the first new destroyer design since the last Clemson was built in 1922. The base ring mount, which improved the effective rate of fire, entered service on USS Porter, commissioned in 1936.

Shell (projectile)

Shell (projectile)

A shell, in a military context, is a projectile whose payload contains an explosive, incendiary, or other chemical filling. Originally it was called a bombshell, but "shell" has come to be unambiguous in a military context. Modern usage sometimes includes large solid kinetic projectiles, which are more properly termed shot. Solid shot may contain a pyrotechnic compound if a tracer or spotting charge is used.

New York-class battleship

New York-class battleship

The New York class was a pair of super-dreadnought battleships built for the United States Navy between 1911 and 1914. The two ships of the class, New York and Texas, saw extensive service beginning in the occupation of Veracruz, World War I, and World War II.

Gunpowder

Gunpowder

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 and potassium nitrate (saltpeter). The sulfur and carbon act as fuels while the saltpeter is an oxidizer. Gunpowder has been widely used as a propellant in firearms, artillery, rocketry, and pyrotechnics, including use as a blasting agent for explosives in quarrying, mining, building pipelines and road building.

Brown powder

Brown powder

Brown powder or prismatic powder, sometimes referred as "cocoa powder" due to its color, was a propellant used in large artillery and ship's guns from the 1870s to the 1890s. While similar to black powder, it was chemically formulated and formed hydraulically into a specific grain shape to provide a slower burn rates with neutral or progressive burning, as opposed to the faster and regressive burn typical of randomly shaped grains of black powder produced by crushing and screening powder formed into sheets in a press box, as was typical for cannon powder previously.

Smokeless powder

Smokeless powder

Smokeless powder is a type of propellant used in firearms and artillery that produces less smoke and less fouling when fired compared to gunpowder. The combustion products are mainly gaseous, compared to around 55% solid products for black powder. In addition, smokeless powder does not leave the thick, heavy fouling of hygroscopic material associated with black powder that causes rusting of the barrel. Despite its name, smokeless powder is not completely free of smoke; while there may be little noticeable smoke from small-arms ammunition, smoke from artillery fire can be substantial.

Poudre B

Poudre B

Poudre B was the first practical smokeless gunpowder created in 1884. It was perfected between 1882 and 1884 at "Laboratoire Central des Poudres et Salpêtres" in Paris, France. Originally called "Poudre V" from the name of the inventor, Paul Vieille, it was arbitrarily renamed "Poudre B" to distract German espionage. "Poudre B" is made from 68.2% insoluble nitrocellulose, 29.8% soluble nitrocellulose gelatinized with ether and 2% paraffin. "Poudre B" is made up of very small paper-thin flakes that are not white but dark greenish grey in colour. "Poudre B" was first used to load the 8mm Lebel cartridges issued in 1886 for the Lebel rifle.

Cordite

Cordite

Cordite is a family of smokeless propellants developed and produced in the United Kingdom since 1889 to replace black powder as a military propellant. Like modern gunpowder, cordite is classified as a low explosive because of its slow burning rates and consequently low brisance. These produce a subsonic deflagration wave rather than the supersonic detonation wave produced by brisants, or high explosives. The hot gases produced by burning gunpowder or cordite generate sufficient pressure to propel a bullet or shell to its target, but not so quickly as to routinely destroy the barrel of the gun.

Nitrocellulose

Nitrocellulose

Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and sulfuric acid. One of its first major uses was as guncotton, a replacement for gunpowder as propellant in firearms. It was also used to replace gunpowder as a low-order explosive in mining and other applications. In the form of collodion it was also a critical component in an early photographic emulsion, the use of which revolutionized photography in the 1860s.

Internal ballistics

Internal ballistics

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

World War I

World War I

World War I or the First World War,, often abbreviated as WWI, was one of the deadliest global conflicts in history. It was fought between two coalitions, the Allies and the Central Powers. Fighting occurred throughout Europe, the Middle East, Africa, the Pacific, and parts of Asia. An estimated 9 million soldiers were killed in combat, plus another 23 million wounded, while 5 million civilians died as a result of military action, hunger, and disease. Millions more died as a result of genocide, while the 1918 Spanish flu pandemic was exacerbated by the movement of combatants during the war.