The Powder
Regardless of the type of firearm being used, some type of propellant is required to launch the projectile toward its target. The earliest successful propellant was a combination of potassium nitrate, charcoal, and sulphur that has come to be known as “black powder.” Friar Roger Bacon (1214-1294) is credited with developing the first compound chemically similar to the “gunpowder” which was to remain in use for the next five centuries. Although the percentages of these chemicals changed slightly as gunpowder evolved, this mixture has remained relatively constant since the early 1780s. This type of propellant is still in wide spread use today among muzzle loading enthusiasts, historical reenactment groups, and others with a nostalgic bent. Today, the sports of “Black Powder Cartridge Rifle” silhouette and “Cowboy Action” shooting are attracting huge numbers of shooters, keeping interest in this timeless propellant alive. Black powder played a vital role in firearms history and development, and due to its low operating pressure, is still appropriate to certain uses.
The chemical composition of the various black powders are essentially identical, leaving the geometry, or granulation, to determine the suitability of a particular powder to a given task. The four most commonly used granulations are graded as FFFFg, FFFg, FFg, and Fg, with FFFFg being the finest and Fg the coarsest. There are (or were) other grades as well, but these are rarely seen today. In general, FFFFg grade powder is used as a priming charge in flintlocks. Coarser grades such as FFFg and FFg are used in revolvers and small to medium bore rifles, while the large Fg grade is used for shotguns and large bore rifles.
Despite its successful use, black powder had several serious drawbacks for both military and sporting usage. It is a very dirty propellant, which leaves large amounts of residue in the bore. This residue degrades accuracy and especially in the case of muzzle loaders (where the projectile must be pushed past the fouling), makes loading the gun for follow up shots progressively more difficult. Cleaning weapons fired with black powder is an arduous and time consuming chore, but must be done promptly due to the powder’s corrosive nature. Firing weapons loaded with black powder also generates copious amounts of white smoke, both plainly marking the firer’s location and obscuring his target from view. It is inefficient, generating relatively small amounts of gas and low pressures for the amount of powder consumed. This in turn limits the velocities that may be attained, without making the firearm so large as to be unwieldy. Black powder is extremely easy to ignite, which makes it dangerous to produce, store, and handle. These problems were addressed as more modern propellant powders were developed.
Between 1846 and 1860, significant advances were made in the development of nitrated cotton and other cellulose fibers, laying the real groundwork for our modern propellants. The first true smokeless propellants were produced in 1884 by the French chemist, Vieille, then in the service of the French government. In 1887, Sweden’s Alfred Nobel invented a smokeless powder comprised of nitrocellulose collided with nitroglycerin. Oddly enough, when these two violent explosives were combined, they formed a well controlled propellant. Nobel named this new powder “Ballisite.” In the same decade, the British developed a very similar propellant that they termed “Cordite.” As smokeless propellants came to be used in military cartridges such as the 8mm Lebel and .303 British, the die was cast, and black powder was rendered obsolete.
Modern smokeless propellants usually fall into one of two basic categories; single base and double base. These designations describe the chemical makeup of the propellants, with single based powders being comprised primarily of nitro-cellulose, and double based powders being made up of a combination of nitro-cellulose and nitroglycerine. Both types are still in widespread use today and are produced by a variety of domestic and foreign manufacturers. There are triple based powders as well, but these are limited almost exclusively to military applications and are virtually unknown among reloaders.
Within the two primary categories, single and double based, there is a wide variety of powder types, defined by geometry or shape. Some of the most common types in use today are flake, extruded tubular, and ball or spherical propellants. Regardless of the type of powder being discussed, its suitability to a given task is determined by its burning rate. Whereas black powder’s burning rate was controlled to a very limited degree by granulation, smokeless propellants are produced in a wide spectrum of burning rates. The IMR series of powders, for example, is a family of powders that are chemically very similar. Their fast burning powders such as IMR-4227 will produce virtually the same amount of gas volume and energy as their slow burning powders, such as IMR-7828. The real difference here, is the amount of time over which the powder will release its energy. Despite their chemical similarity, the burning rate of these powders can be controlled to suit the needs of a small case calling for a very “fast” powder, or a large magnum type case calling for a very “slow” burning powder. Aside from very minor chemical differences, the burning rate of the various powders is largely controlled by the size and shape (surface area), and the use of deterrent coatings such as dinitro-toluene (DNT). These charges are applied to the kernels of powder in varying degrees to control the burning characteristics of the finished product.