Cordite

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A stick of cordite from World War II.
A sectioned British 18 pounder field gun shrapnel round, World War I, showing string bound to roughly simulate the appearance of the cordite propellant
Sticks of cordite from a .303 British rifle cartridge.

Cordite is a family of smokeless propellants developed and produced in the United Kingdom since 1889 to replace gunpowder as a military propellant. Like 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 firearm, or gun.

Cordite was used initially in the .303 British, Mark I and II, standard rifle cartridge between 1891 and 1915; shortages of cordite in World War I led to United States–developed smokeless powders being imported into the UK for use in rifle cartridges. Cordite was also used for large weapons, such as tank guns, artillery and naval guns. It has been used mainly for this purpose since the late 19th century by the UK and British Commonwealth countries. Its use was further developed before World War II, and as 2-and-3-inch-diameter (51 and 76 mm) Unrotated Projectiles for launching anti-aircraft weapons. Small cordite rocket charges were also developed for ejector seats made by the Martin-Baker Company. Cordite was also used in the detonation system of the Little Boy atomic bomb dropped over Hiroshima in August 1945.

The term cordite generally disappeared from official publications between the wars. During World War II double based propellants were very widely used and there was some use of triple based propellants by artillery. Triple based propellants were used in post-war ammunition designs and remain in production for UK weapons; most double based propellants left service as World War II stocks were expended after the war. For small arms it has been replaced by other propellants, such as the Improved Military Rifle (IMR) line of extruded powder or the WC844 ball propellant currently in use in the 5.56×45mm NATO. Production ceased in the United Kingdom, around the end of the 20th century, with the closure of the last of the World War II cordite factories, ROF Bishopton. Triple base propellant for UK service (for example, the 105 mm L118 Light Gun) is now manufactured in Germany.

Adoption of smokeless powder by the British government[edit]

Replacements for gunpowder (black powder)[edit]

Gunpowder, an explosive mixture of sulfur, charcoal and potassium nitrate (also known as saltpetre/saltpeter), was the original gun propellant employed in firearms and fireworks. It was used from about 10th or 11th century onwards, but it had disadvantages, including the large quantity of smoke it produced. With the 19th-century development of various "nitro explosives", based on the reaction of nitric acid mixtures on materials such as cellulose and glycerine, a search began for a replacement for gunpowder.

Early European smokeless powders[edit]

The first smokeless powder was developed in 1865 by Major Johann F. E. Schultze of the Prussian artillery. His formulation (dubbed Schultze Powder) comprised nitrolignose impregnated with saltpetre or barium nitrate.

In 1882 the Explosive Company of Stowmarket introduced EC Powder, which contained nitro-cotton and nitrates of potassium and barium in a grain gelatinesed by ether alcohol. It had coarser grains than other nitrocellulose powders. It proved unsuitable for rifles, but it remained in long use for shotguns and was later used for grenades and fragmentation bombs.

In 1884, the French chemist Paul Vieille produced a smokeless propellant that had some success. It was made out of collodion (nitrocellulose dissolved in ethanol and ether), resulting into a plastic colloidal substance which was rolled into very thin sheets, then dried and cut up into small flakes. It was immediately adopted by the French military for their Mle 1886 infantry rifle and called Poudre B (for Poudre Blanche, or "White Powder") to distinguish it from "Black Powder" (gunpowder). The rifle and the cartridge developed to use this powder were known generically as the 8mm Lebel, after the officer who developed its 8 mm full metal jacket bullet.

The following year, 1887, Alfred Nobel invented and patented a smokeless propellant he called Ballistite. It was composed of 10% camphor, 45% nitroglycerine and 45% collodion (nitrocellulose). Over time the camphor tended to evaporate, leaving an unstable explosive.

Development of Cordite[edit]

Sir James Dewar at work

A United Kingdom government committee, known as the "Explosives Committee", chaired by Sir Frederick Abel, monitored foreign developments in explosives and obtained samples of Poudre B and Ballistite; neither of these smokeless powders was recommended for adoption by the Explosives Committee.

Abel, Sir James Dewar and Dr W Kellner, who was also on the committee, developed and jointly patented (Nos 5,614 and 11,664 in the names of Abel and Dewar) in 1889 a new ballistite-like propellant consisting of 58% nitroglycerine, by weight, 37% guncotton (nitrocellulose) and 5% petroleum jelly. Using acetone as a solvent, it was extruded as spaghetti-like rods initially called "cord powder" or "the Committee's modification of Ballistite", but this was swiftly abbreviated to "Cordite".

Cordite began as a double-base propellant. In the 1930s triple-base was developed by including a substantial proportion of nitroguanidine. Triple-based propellant reduced the disadvantages of double-base propellant - its relatively high temperature and significant flash, by combining two high explosives: nitrocellulose and nitroglycerine. Imperial Chemical Industries's (ICI) World War 2 double-base AN formulation also had a much lower temperature, but it lacked the flash reduction properties of N and NQ triple-base propellants.

Whilst cordite is classified as an explosive, it is not employed as a high explosive. It is designed to deflagrate, or burn, to produce high pressure gases.

Nobel and Abel patent dispute[edit]

Alfred Bernhard Nobel sued Abel and Dewar over an alleged patent infringement. His patent specified that the nitrocellulose should be "of the well-known soluble kind". After losing the case, it went to the Court of Appeal. This dispute eventually reached the House of Lords, in 1895, but it was finally lost because the words "of the well-known soluble kind" in his patent were taken to mean the soluble collodion, and hence specifically excluded the insoluble guncotton. The ambiguous phrase was "soluble nitro-cellulose": soluble nitro-cellulose was known as Collodion and was soluble in alcohol. It was employed mainly for medical and photographic use. In contrast, insoluble, in alcohol, nitrocellulose was known as gun cotton and was used as an explosive. Nobel's patent refers to the production of Celluloid using camphor and soluble nitrocellulose; and this was taken to imply that Nobel was specifically distinguishing between the use of soluble and insoluble nitrocellulose.