Propellant - Until the end of the 19th century,all cartridges were loaded with black powder.Black powder is a mixture of charcoal,sulfur and potassium nitrate.These materials were individually ground to a powder,mechanically mixed,ground together,incorporated with help of moisture and pressed into hard cakes,dried and then broken down into the desired granulation.In such a mixture,the charcoal is the fuel,the potassium nitrate,the oxygen supplier or oxidizer while the sulfur gives the mixture more density and workability and makes it more readily ignitable.When black powder burns properly,it produces 44% of its original weight in gases and 56% in solid residues.These residues appear principally as a dense white smoke.
In 1887, Vieille, a French chemist, first synthesized an effective practical form of what is now known as smokeless powder.Using alcohol and ether, he reduced nitrocellulose to a gelatinous colloid which was rolled into sheets and cut into flakes.In 1887, Alfred Nobel developed a slightly different form of smokeless powder.Utilizing nitrocellulose that was not highly nitrated as that used by Vieille, he colloided it with nitroglycerine and then dried, rolled and cut it into flakes.These two types of smokeless powder are known as single-base and double-base powders respectively.The physical configuration of individual powder grains can be disk,flake,or cylinder, whether the powder is single or double base.
The next major step in the development of smokeless powder was the introduction of ball powder by Winchester in 1933.In ball powder, the nitrocellulose instead of being colloided is dissolved completely and the resultant lacquer is agitated under conditions to make it form into small balls that constitute the powder grains.By manipulation of the process, the diameter of the balls of powder can be controlled whereas in an extra operation, the balls of powder may be flattened between the rollers, thus altering the surface and thus the burning rate of the powder.True ball powder appears as small, uniform silver-black spheres or ovals having a shiny, reflective surface, flattened ball powder as irregular flattened chips with a silver-black shiny surface.In most flattened ball powder, one can find non-flattened spheres and ovoid grains.Between the extremes of true ball and flattened ball powder is a wide spectrum of physical variations.
Smokeless powder is theoretically converted completely into gaseous products.Unlike black powder, it does not leave a significant residue in the bore.Smokeless powder burns at the surface only thus, the burning surface decreases continuously as the grains are consumed.This degressive burning, an unfavorable characteristic, can be overcome to a degree by putting a hole in the individual powder grain with a resultant increase in the surface area as the grain burns.More commonly, chemical coating deterrents are applied to powder grains to slow the burning initially in order to make progressive burning powder.These grains of powder burns slowly at first and then rapidly.The grains of powder may also be coated with graphite to eliminate static electricity and facilitate the flow of powder while the cartridges are loaded.Rather than having a shiny black appearance, uncoated grains of powder are a pale-green color.Powder grains recovered from the skin or clothing after discharge of a gun may not be black but rather pale-green or beige due to loosing the coating.
The weight of the propellant charge in a cartridge is adjusted for each lot of propellant to give the required muzzle velocity for the weight of the bullet with a chamber pressure within the limit prescribed for the weapon.Pyrodex, a synthetic black powder, was developed to replace black powder in weapon in which only black powder can be used.It was developed for two reasons, first, there is a shortage of black powder and second, there are a number of restrictions in the U.S. put on the sale and storage of black powder because of its explosive properties.As pyrodex is a nitrocellulose based powder, it is considerably safer than black powder and avoids these restrictions.The problem with developing a replacement for black powder is that black powder burns at substantially the same rate whether unconfined or fired in a weapon.Smokeless powder however, burns slowly when unconfined, requiring about 1000 lbs/in. of pressure to burn consistently.As pressure increases, it burns at an increasing rate, producing pressures that exceed those that can be tolerated by black powder firearms.
Pyrodex has more bulk than black powder, with an equal volume of pyrodex having about 88% of the weight of black powder.In weapons chambered for black powder, pyrodex is loaded bulk for bulk with black powder, not by weight.The pressures and velocities generated are thus compatible with those achieved with black powder.