Science Fair Project Encyclopedia
Smokeless powder is the name given to any number of gunpowder-like propellants used in firearms which produce neglegible smoke when fired, unlike the older black powder which it replaced. Types of smokeless powder include cordite, ballistite and, historically, Poudre B.
Smokeless powder consists of almost pure nitrocellulose (single-base powders), frequently combined with up to 50 percent nitroglycerin (double-base powders), and sometimes nitroguanidine (triple-base) corned into small spherical balls or extruded into cylinders or flakes using solvents such as ether. The reason that it is smokeless is that the combustion products are mainly gaseous, compared to around 60% solid products for black powder (potassium carbonate, potassium sulfate etc).
Smokeless powder burns only on the surfaces of the granules. 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). 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.
Military commanders had been complaining since the Napoleonic Wars about the problems of giving orders on a battlefield that was covered in thick smoke from the gunpowder used by the guns. A major step forward was introduced when guncotton, a nitrocellulose-based propellant, was widely introduced in 1846. Guncotton was more powerful than gunpowder, but at the same time was somewhat more volatile. 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 be "used up" after only a few hundred with the more powerful guncotton. It did find wide use with artillery however.
In 1886 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. The resulting propellant, today known as pyrocellulose, contains somewhat less nitrogen than guncotton and is less volatile. A particularly nice feature of the propellant is that it would not burn unless it was compressed, making it very safe to handle under normal conditions.
Vieille's powder revolutionized the effectiveness of small guns, for the following reasons:
- It gave off almost no smoke. After a few shots, a soldier with black powder ammunition would have his view obscured by a huge pall of smoke unless there was a strong wind.
- It was three times more powerful than black powder. This gave two advantages:
- The 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.
- A round of ammunition needed less powder, so its calibre could be reduced, making it lighter. This allowed troops to carry more ammunition for the same weight.
- It would detonate even when wet. This was less of a problem in the mid-19th century though, when black powder ammunition was contained 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 1887 Alfred Nobel developed a smokeless gunpowder called ballistite. 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 patent infringement. Both explosives were more stable and thus safer to handle than Poudre B, and also more powerful. Today propellants based on nitrocellulose alone are known as single-base, whereas cordite-like mixtures are known as double-base. A triple-base flashless cordite was also developed, primarily for large naval guns.
Smokeless powder allowed the development of modern semi- and fully automatic firearms. Burned blackpowder leaves a thick, heavy fouling which is both hygroscopic and corrosive. Smokeless powder fouling exhibits none of these properties. This makes feasible an autoloading firearm with many moving parts (which would jam or seize under heavy blackpowder fouling).
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.
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