Smokeless powder
is the 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. 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.
[Hatcher, Julian S. and Barr, Al Handloading Hennage Lithograph Company (1951) p.34] Despite its name smokeless powder is actually not completely
smoke-free
[Fairfield, A. P., CDR USN Naval Ordnance Lord Baltimore Press (1921) p.44] and does not take the form of a true
powder (see
granular material). Smokeless powder allowed the development of modern semi- and fully automatic firearms. Burnt blackpowder leaves a thick, heavy
fouling which is both
hygroscopic and
corrosive. Smokeless powder fouling exhibits none of these properties. This makes an autoloading firearm with many moving parts feasible (which would otherwise jam or seize under heavy blackpowder 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, so 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 gunnery battlefield. 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. After a few shots, soldiers using black powder ammunition would have their view obscured by a huge pall of smoke unless there was a strong wind.
Snipers or other concealed shooters were given away by a cloud of smoke over the firing position.
A major step forward was introduced when
guncotton, a
nitrocellulose-based material, was first introduced by
Christian Friedrich Schönbein in 1846. He also promoted its use as a blasting explosive.
[Davis, William C., Jr. Handloading National Rifle Association of America (1981) p.28] 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 1884,
Paul Vieille invented a smokeless gunpowder called
Poudre B, made from gelatinized guncotton mixed with
ether and
alcohol. It was passed through rollers to form thin sheets, which were cut into flakes of the desired size.
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) pages 289–292] 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 therefore more accurate long range fire, out to perhaps 1000 metres in the first smokeless powder rifles. 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.
Vielle's powder was used in the
Lebel rifle that was immediately introduced by the
French Army to exploit its huge benefits over black powder. 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.
Meanwhile, in
Great Britain, in 1887,
Alfred Nobel developed a smokeless gunpowder called
Ballistite.
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) p.293] A modified form of this was devised by Sir
Frederick Abel and
James Dewar which eventually became known as
Cordite, leading to a lengthy court battle between Nobel and the other two inventors over alleged British
patent infringement. In the
USA, in 1890, a patent for smokeless powder was obtained by
Hudson Maxim.
Chemical variations
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,
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) p.297] whereas cordite-like mixtures using
nitroglycerin to dissolve the nitrocellulose are known as
double-base powder.
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) p.298] Single and double-base smokeless powders now make up the vast majority of propellants used in firearms. They are so common that most modern references to
gunpowder refer to a smokeless powder, particularly when referring to
small arms ammunition. A
triple-base powder including
nitroguanidine was developed as a flashless cordite primarily for large
naval guns, but also used in battle
tank ammunition.
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 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.
[Fairfield, A. P., CDR USN Naval Ordnance Lord Baltimore Press (1921) p.28][Davis, Tenny L. The Chemistry of Powder & Explosives (1943) p. 310] 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 on the remaining amount of stabilizer, as its depletion may lead to auto-ignition of the propellant.
Physical variations
Smokeless powder may be corned into small spherical balls or
extruded into cylinders or flakes using solvents such as ether. The properties of the propellant are greatly influenced by the size and shape of its grains. The surface of the grains influences the speed of burning, and the shape influences the surface and its change during burning. By selection of the grain shape it is possible to influence the pressure vs time curve as the propellant burns. Smokeless powder burns only on the surfaces of the granules, flakes or cylinders (described as
granules for short). Larger granules 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.
Cannon powder has the largest granules, up to thumb-sized cylinders with seven perforations (one central and the other six in a circle halfway to the outside of the cylinder's end faces). 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).
[Fairfield, A. P., CDR USN Naval Ordnance Lord Baltimore Press (1921) pp.41-43] 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.
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) p.306]Faster-burning propellants generate higher temperatures and higher pressures, however they also increase the wear of the gun barrels.
Smokeless propellant components
The propellant formulations may contain various energetic and auxiliary components:
- * Nitrocellulose, an energetic component of most smokeless propellants
[Campbell, John Naval Weapons of World War Two (1985) p. 5]
- * Nitroglycerin, an energetic component of double-base and triple-base formulations
- * D1NA (bis-nitroxyethylnitramine)
[Campbell, John Naval Weapons of World War Two (1985) p. 104]
- * Fivonite (tetramethylolcyclopentanone)
- * DGN (di-ethylene glycol dinitrate)
[Campbell, John Naval Weapons of World War Two (1985) p. 221]
- * Acetyl cellulose
[Campbell, John Naval Weapons of World War Two (1985) p. 318]
- Deterrents, (or moderants), to slow the burning rate
- * Centralites (symmetrical diphenyl urea -- primarily diethyl or dimethyl)
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) pages 317-320][Davis, William C., Jr. Handloading National Rifle Association of America (1981) p.30]
- * Dinitrotoluene (toxic, carcinogenic, and obsolete)
[Davis, William C., Jr. Handloading National Rifle Association of America (1981) p.31]
- * Akardite (asymmetrical diphenyl urea)
- * ortho-tolyl urethane
[Campbell, John Naval Weapons of World War Two (1985) p. 174]
- Stabilizers, to prevent or slow down self-decomposition
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) pages 307–311]
- * Diphenylamine
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) p. 302]
- * Petroleum jelly
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) p. 296]
- * beta-naphthol methyl ether
- * Amyl alcohol (obsolete)
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) p. 307]
- * Aniline (obsolete)
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) p. 308]
- Decoppering additives, to hinder the buildup of copper residues from the gun barrel rifling
- * Tin metal and compounds (e.g., tin dioxide)
[Davis, William C., Jr. Handloading National Rifle Association of America (1981) p.32]
- * 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)
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) pages 322–327]
- * Potassium chloride
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) pages 323-327]
- * 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
- * Rosin, a surfactant to hold the grain shape of spherical powder
Manufacturing
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.
[Fairfield, A. P., CDR USN Naval Ordnance Lord Baltimore Press (1921) pages 28-31]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.
[Fairfield, A. P., CDR USN Naval Ordnance Lord Baltimore Press (1921) pages 31-35]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.
[Fairfield, A. P., CDR USN Naval Ordnance Lord Baltimore Press (1921) pages 35-41][Davis, Tenny L. The Chemistry of Powder & Explosives (1943) pages 293 & 306]Military quantities of old smokeless powder were sometimes reworked into new lots of propellants.
[Fairfield, A. P., CDR USN Naval Ordnance Lord Baltimore Press (1921) p.39] Through the 1920's 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.
[Matunas, E. A. Winchester-Western Ball Powder Loading Data Olin Corporation (1978) p.3] 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.
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) pages 328-330][Wolfe, Dave Propellant Profiles Volume 1 Wolfe Publishing Company (1982) pages 136-137]Flashless Powder
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 suppression was attempted by structural modification of the muzzle of small arms. This approach was less successful for artillery, where a flame extending 150 feet (50 meters) from the muzzle might be reflected off clouds and be visible for distances up to 30 miles (50 kilometers).
[Davis, Tenny L. The Chemistry of Powder & Explosives (1943) pages 322-323]Flash suppression was achieved by smokeless powder additives. Cooler burning explosives like nitroguanidine or ammonium nitrate were added to reduce the temperature of combustion gasses. Inorganic salts like potassium chloride were added 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.
Primex Powder
A Primex powder contains:
- 0-1.5% N-nitrosodiphenylamine,
- 0-1.5% 2-nitrodiphenylamine,
- 0-1.5% potassium nitrate,
- 0-1.5% potassium sulfate,
with nitrocellulose accounting for the remainder.
See also
- Brown-brown - a drug created by mixing cocaine with cartridge powder
