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 powders corrosive nature.
Firing weapons loaded with black powder also generates copious amounts
of white smoke, both plainly marking the firers 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, Swedens 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 powders 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.
|