Smokeless powder

Smokeless powder

Smokeless powder is name given to a number of propellants used in firearms and artillery which produce negligible smoke when fired, unlike the older gunpowder (black powder) which they replaced. It remains in general use in the United States but rest of the English speaking world has not used it since the 19th century and uses Propellant. The basis of the term smokeless is that the combustion products are mainly gaseous, compared to around 55% solid products (mostly potassium carbonate, potassium sulfate, and potassium sulfide) for black powder. Despite its name, smokeless powder is not completely smoke-free, while there may be little noticeable smoke from small-arms ammunition, smoke from artillery fire can be substantial.

Since the 14th century gunpowder was not actually a physical "powder," and smokeless powder can only be produced as a pelletized or extruded granular material. Smokeless powder allowed the development of modern semi- and fully automatic firearms and lighter breeches and barrels for artillery. Burnt black powder leaves a thick, heavy fouling which is hygroscopic and causes rusting of the barrel. The fouling left by smokeless powder exhibits none of these properties. This makes an autoloading firearm with many moving parts feasible (which would otherwise jam or seize under heavy black powder fouling).

Smokeless powders are classified as, typically, division 1.3 explosives under the UN Recommendations on the transportation of Dangerous goods - Model Regulations, regional regulations (such as ADR) and national regulations (such the United States' ATF). However, they are used as solid propellants; in normal use, they undergo deflagration rather than detonation.

Background

Military commanders had been complaining since the Napoleonic Wars about the problems of giving orders on a battlefield obscured by the smoke of firing. Verbal commands could not be heard above the noise of the guns, and visual signals could not be seen through the thick smoke from the gunpowder used by the guns. Unless there was a strong wind, after a few shots, soldiers using black powder ammunition would have their view obscured by a huge cloud of smoke. Snipers or other concealed shooters were given away by a cloud of smoke over the firing position. Black powder is also corrosive, making cleaning mandatory after every use. Likewise, black powder's tendency to produce severe fouling caused actions to jam and often made reloading difficult.

A major step forward was the discovery of guncotton, a nitrocellulose-based material, by Christian Friedrich Schönbein in 1846. He also promoted its use as a blasting explosive. Guncotton was more powerful than gunpowder, but at the same time was somewhat more unstable. This made it unsuitable as a propellant for small firearms: not only was it dangerous under field conditions, but guns that could fire thousands of rounds using gunpowder would reach their service life after only a few hundred with the more powerful guncotton. It did find wide use with artillery. However, within a short time there were a number of massive explosions and fatalities in guncotton factories due to lack of appreciation of its sensitivity and the means of stabilization. Guncotton then went out of use for some twenty years or more until it could be tamed; it was not until the 1880s that it became a viable propellant.

19th century improvements

In 1863 Sir Fredeick Abel in England began thorough research that led to manufacturing process that eliminated the impurities in nitrocellulose making it safer to produce and a stable product safer to handle. However, while this guncotton was a useful high explosive it was not suitable as a propellant. Nitroglycerine was discovered by Professor Sobrero in Turing in 1846 subsequently developed and manufactured by Alfred Nobel but it too was unsuitable as a propellant. The first successful smokeless powder was produced by Major Schultze of the Prussian artillery in 1865. It was a form of nitrolignose impregnated with saltpetre or barium nitrate. Another formulation was produced by the Explosives Company at Stowmarket in England in 1882, it used nitro-cotton and nitrates of potassium and barium and gelatinised by ether-alcohol. As a propellant this was suitable for shotguns but not rifles.

In 1884, Paul Vieille invented a smokeless gunpowder called Poudre B after General Boulanger, made from 68.2% insoluble nitrocellulose, 29.8% soluble nitrocelusose gelatinized with ether and 2% paraffin. This was adopted for the Lebel rifle. It was passed through rollers to form paper thin sheets, which were cut into flakes of the desired size. The resulting propellant, today known as pyrocellulose, contains somewhat less nitrogen than guncotton and is less volatile. A particularly good feature of the propellant is that it will not detonate unless it is compressed, making it very safe to handle under normal conditions.

Vieille's powder revolutionized the effectiveness of small guns, because it gave off almost no smoke and was three times more powerful than black powder. Higher muzzle velocity meant a flatter trajectory and less wind drift and bullet drop, making 1000 meter shots practicable. Since less powder was needed to propel a bullet, the cartridge could be made smaller and lighter. This allowed troops to carry more ammunition for the same weight. Also, it would burn even when wet. Black powder ammunition had to be kept dry and was almost always stored and transported in watertight cartridges.

Other European countries swiftly followed and started using their own versions of Poudre B, the first being Germany and Austria which introduced new weapons in 1888. Subsequently Poudre B was modified several times with various compounds being added and removed.

Meanwhile, in 1887, Alfred Nobel developed a smokeless gunpowder he called Ballistite. In this propellant the fibrous structure of cotton (nitro-cellulose) was destroyed by a nitro-glycerine solution instead of a solvent.

The Germans adopted ballisite for naval use in 1898, calling it WPC/98. The Italian adopted it as 'filite', in cord instead of flake form, but realising its drawbacks changed to a formulation with nitroglycerine they called 'solenite'. In 1891 the Russians tasked the chemist Mendeleef with finding a suitable propellant, he created nitrocellulose gelatinised by ether-alcohol, which produced more nitrogen and more uniform colloidal structure than the French use of nitro-cottons in Poudre B. He called it pyro-collodion. After experimenting with various types of propellant the United States adopted a pyro-collodion. In the USA, in 1890, a patent for smokeless powder was obtained by Hudson Maxim.

Britain conducted trials on all the various types of propellant brought to their attention, but were dissatified with them all and sought soemething superior to all existing types. In 1889 Sir Frederick Abel, James Dewar and Dr W Kellner patented (Nos 5614 and 11,664 in the names of Abel and Dewar) a new formulation that was manufactured at the Royal Gunpowder Factory at Waltham Abbey. It entered British service in 1891 as Cordite Mark 1. Its main composition was 58% Nitro-glycerine, 37% Guncotton and 3% mineral jelly. A modified version, Cordite MD, entered service in 1901, this increased guncotton to 65% and reduced nitro-glycerine to 30%, this change reduced the combustion temperature and hence erosion and barrel wear. Cordites' advantages over gunpowder were reduced maximum pressure in the chamber (hence lighter breeches, etc.) but longer high pressure. Cordite could be made in any desired shape or size.

The creation of cordite led to a lengthy court battle between Nobel and the other two inventors over alleged British patent infringement.

Chemical variations

"Double base" redirects here. For the musical instrument, see double bass.

These newer propellants were more stable and thus safer to handle than Poudre B, and also more powerful. Today, propellants based on nitrocellulose alone (typically an ether-alcohol colloid of nitrocellulose) are described as single-base powder, whereas cordite-like mixtures using nitroglycerin to dissolve the nitrocellulose are known as double-base powder.

During the 1930s triple-base propellant which included a substantial quantity of nitroguanidine was developed. It had reduced flash compared to single and double base, albeit at the cost of more smoke. During World War II it had some use by British artillery, after that war it became the standard propellant in all British ammunition designs except small-arms. Most western nations, except the United States, followed a similar path.

In the late 20th century new propellant formulations started to appear. These are based on nitroguanidine and high explosives of the RDX type.

Instability and stabilization

Nitrocellulose deteriorates with time, yielding acidic byproducts. Those byproducts catalyze the further deterioration, increasing its rate. The released heat, in case of bulk storage of the powder, or too large blocks of solid propellant, can cause self-ignition of the material. Single-base nitrocellulose propellants are hydroscopic and most susceptible to degradation; double-base and triple-base propellants tend to deteriorate more slowly. To neutralize the decomposition products, which could otherwise cause corrosion of metals of the cartridges and gun barrels, calcium carbonate is added to some formulations.

To prevent buildup of the deterioration products, stabilizers are added. Diphenylamine is one of the most common stabilizers used. Nitrated analogs of diphenylamine formed in the process of stabilizing decomposing powder are sometimes used as stabilizers themselves. The stabilizers are added in the amount of 0.5-2% of the total amount of the formulation; higher amounts tend to degrade its ballistic properties. The amount of the stabilizer is depleted with time. Propellants in storage should be periodically tested for the amount of stabilizer remaining, as its depletion may lead to auto-ignition of the propellant.

Physical variations

Ammunition handloading powders

Smokeless powder may be corned into small spherical balls or extruded into cylinders or strips with many cross-sectional shapes (strips with various rectangular proportions, single or multi-hole cylinders, slotted cylinders) using solvents such as ether. These extrusions can be cut into short ('flakes') or long pieces ('cords' many inches long). Cannon powder has the largest pieces.

The properties of the propellant are greatly influenced by the size and shape of its pieces. The specific surface area of the propellant influences the speed of burning, and the size and shape of the particles determine the specific surface area. By manipulation of the shape it is possible to influence the burning rate and hence the rate at which pressure builds during combustion. Smokeless powder burns only on the surfaces of the pieces. Larger pieces burn more slowly, and the burn rate is further controlled by flame-deterrent coatings which retard burning slightly. The intent is to regulate the burn rate so that a more or less constant pressure is exerted on the propelled projectile as long as it is in the barrel so as to obtain the highest velocity. The perforations stabilize the burn rate because as the outside burns inward (thus shrinking the burning surface area) the inside is burning outward (thus increasing the burning surface area, but faster, so as to fill up the increasing volume of barrel presented by the departing projectile). Fast-burning pistol powders are made by extruding shapes with more area such as flakes or by flattening the spherical granules. Drying is usually performed under a vacuum. The solvents are condensed and recycled. The granules are also coated with graphite to prevent static electricity sparks from causing undesired ignitions.

Faster-burning propellants generate higher temperatures and higher pressures, however they also increase wear on gun barrels.

Smokeless propellant components

The propellant formulations may contain various energetic and auxiliary components:

• Propellants:
  • Nitrocellulose, an energetic component of most smokeless propellants
  • Nitroglycerin, an energetic component of double-base and triple-base formulations
  • Nitroguanidine, a component of triple-base formulations
  • D1NA (bis-nitroxyethylnitramine)
  • Fivonite (tetramethylolcyclopentanone)
  • DGN (di-ethylene glycol dinitrate)
  • Acetyl cellulose
• Deterrents, (or moderants), to slow the burning rate
  • Centralites (symmetrical diphenyl urea—primarily diethyl or dimethyl)
  • Dibutyl phthalate
  • Dinitrotoluene (toxic, carcinogenic, and obsolete)
  • Akardite (asymmetrical diphenyl urea)
  • ortho-tolyl urethane
  • Polyester adipate
  • Camphor (obsolete)
• Stabilizers, to prevent or slow down self-decomposition
  • Diphenylamine
  • Petroleum jelly
  • Calcium carbonate
  • Magnesium oxide
  • Sodium bicarbonate
  • beta-naphthol methyl ether
  • Amyl alcohol (obsolete)
  • Aniline (obsolete)
• Decoppering additives, to hinder the buildup of copper residues from the gun barrel rifling
  • Tin metal and compounds (e.g., tin dioxide)
  • Bismuth metal and compounds (e.g., bismuth trioxide, bismuth subcarbonate, bismuth nitrate, bismuth antimonide); the bismuth compounds are favored as copper dissolves in molten bismuth, forming brittle and easily removable alloy
  • Lead foil and lead compounds, phased out due to toxicity
• Flash reducers, to reduce the brightness of the muzzle flash (all have a disadvantage: the production of smoke)
  • Potassium chloride
  • Potassium nitrate
  • Potassium sulfate
  • Potassium hydrogen tartarate (a byproduct of wine production formerly used by French artillery)
• Wear reduction additives, to lower the wear of the gun barrel liners
  • Wax
  • Talc
  • Titanium dioxide
  • Polyurethane jackets over the powder bags, in large guns
• Other additives
  • Ethyl acetate, a solvent for manufacture of spherical powder
  • Rosin, a surfactant to hold the grain shape of spherical powder
  • Graphite, a lubricant to cover the grains and prevent them from sticking together, and to dissipate static electricity

Manufacturing

This section describes procedures used in the United States. See Cordite for alternative procedures formerly used in the United Kingdom.

The United States Navy manufactured single-base tubular powder for naval artillery at Indian Head, Maryland, beginning in 1900. Similar procedures were used for United States Army production at Picatinny Arsenal beginning in 1907 and for manufacture of smaller grained Improved Military Rifle (IMR) powders after 1914. Short-fiber cotton linter was boiled in a solution of sodium hydroxide to remove vegetable waxes, and then dried before conversion to nitrocellulose by mixing with concentrated nitric and sulfuric acids. Nitrocellulose still resembles fibrous cotton at this point in the manufacturing process, and was typically identified as pyrocellulose because it would spontaneously ignite in air until unreacted acid was removed. The term guncotton was also used; although some references identify guncotton as a more extensively nitrated and refined product used in torpedo and mine warheads prior to use of TNT.

Unreacted acid was removed from pyrocellulose pulp by a multistage draining and water washing process similar to that used in paper mills during production of chemical woodpulp. Pressurized alcohol removed remaining water from drained pyrocellulose prior to mixing with ether and diphenylamine. The mixture was then fed through a press extruding a long turbular cord form to be cut into grains of the desired length.

Alcohol and ether were then evaporated from "green" powder grains to a remaining solvent concentration between 3 percent for rifle powders and 7 percent for large artillery powder grains. Burning rate is inversely proportional to solvent concentration. Grains were coated with electrically conductive graphite to minimize generation of static electricity during subsequent blending. "Lots" containing more than ten tonnes of powder grains were mixed through a tower arrangement of blending hoppers to minimize ballistic differences. Each blended lot was then subjected to testing to determine the correct loading charge for the desired performance.

Military quantities of old smokeless powder were sometimes reworked into new lots of propellants. Through the 1920s Dr. Fred Olsen worked at Picatinny Arsenal experimenting with ways to salvage tons of single-base cannon powder manufactured for World War I. Dr. Olsen was employed by Western Cartridge Company in 1929 and developed a process for manufacturing spherical smokeless powder by 1933. Reworked powder or washed pyrocellulose can be dissolved in ethyl acetate containing small quantities of desired stabilizers and other additives. The resultant syrup, combined with water and surfactants, can be heated and agitated in a pressurized container until the syrup forms an emulsion of small spherical globules of the desired size. Ethyl acetate distills off as pressure is slowly reduced to leave small spheres of nitrocellulose and additives. The spheres can be subsequently modified by adding nitroglycerine to increase energy, flattening between rollers to a uniform minimum dimension, coating with phthalate deterrents to retard ignition, and/or glazing with graphite to improve flow characteristics during blending.

Flashless propellant

Muzzle flash is the light emitted in the vicinity of the muzzle by the hot propellant gases and the chemical reactions that follow as the gases mix with the surrounfing air. Before projectiles exit a slight pre-flash may occur from gases leaking past the projectiles. Following muzzle exit the heat of gases is usually sufficient to emit visibnble radiation - the primary flash. The gases expand but as the pass through the Mach disc they are re-compressed to produce an intermediate flash. Hot combustable gases (e.g. hydrogen and carbon-dioxide) may follow when they mix with oxygen in the surrounding air to produce the secondary flash, the brightest. The secondary flash does not usually occur with small-arms.

Nitrocellulose contains insufficient oxygen to completely oxidize its carbon and hydrogen. The oxygen deficit is increased by addition of graphite and organic stabilizers. Products of combustion within the gun barrel include flammable gasses like hydrogen and carbon monoxide. At high temperature, these flammable gasses will ignite when turbulently mixed with atmospheric oxygen beyond the muzzle of the gun. During night engagements the flash produced by ignition can reveal the location of the gun to enemy forces and cause temporary night-blindness among the gun crew by photo-bleaching visual purple.

Flash suppressors are commonly used on small arms to reduce the flash signature, but this approach is not practical for artillery. Artillery muzzle flash up to 150 feet (50 meters) from the muzzle has been observed, and can be reflected off clouds and be visible for distances up to 30 miles (50 kilometers). For artillery the most effective method is a propellant that produces a large proportion of inert nitrogen at relatively low temperatures that dilutes the combusable gases. Triple based propellants are used for this because of the nitrogen in the nitroguandine.

Before the use of triple based propellants the usual method of flash reduction was to add inorganic salts like potassium chloride so their specific heat capacity might reduce the temperature of combustion gasses and their finely divided particulate smoke might block visible wavelengths of radiant energy of combustion.

See also

• Antique guns
• Ballistite
• Cordite
• Firearms
• Gunpowder
• Nitrocellulose
• Small arms
• Brown-brown – a drug created by mixing cocaine with cartridge powder

References

Sources

• Campbell, John (1985). Naval Weapons of World War Two. Naval Institute Press. ISBN 0-87021-459-4.
• Davis, Tenney L. (1943). The Chemistry of Powder & Explosives (Angriff Press [1992] ed.). John Wiley & Sons Inc. ISBN 0-913022-00-4.
• Davis, William C., Jr. (1981). Handloading. National Rifle Association of America. ISBN 0-935998-34-9.{{cite book}}: CS1 maint: multiple names: authors list (link)
• Fairfield, A. P., CDR USN (1921). Naval Ordnance. Lord Baltimore Press.{{cite book}}: CS1 maint: multiple names: authors list (link)
• Hatcher, Julian S. and Barr, Al (1951). Handloading. Hennage Lithograph Company.{{cite book}}: CS1 maint: multiple names: authors list (link)
• Matunas, E. A. (1978). Winchester-Western Ball Powder Loading Data. Olin Corporation.
• Wolfe, Dave (1982). Propellant Profiles Volume 1. Wolfe Publishing Company. ISBN 0-935632-10-7.

External links

• The Manufacture of Smokeless Powders and their Forensic Analysis: A Brief Review - Robert M. Heramb, Bruce R. McCord