By Chuck Hawks
The stuff that we shooters know as smokeless powder was introduced as a black powder replacement in the 1880's. Besides generating a lot less smoke, smokeless powder burns much cleaner and more efficiently than black powder, greatly reducing powder fouling and increasing the performance of the shotgun, handgun, and rifle cartridges in which it is used. It is also much safer to produce than black powder, which has saved many lives over the years.
Smokeless powders are nitrocellulose-based propellants derived from experiments with guncotton, which was created in the mid-1800's by exposing wood or cotton fibers to nitric acid. Gun cotton is not a suitable propellant, but softening guncotton in a mixture of ether and alcohol produced the first, crude, smokeless powder.
Modern Nitrocellulose powders have come a long way since then. Today there are single-base and double-base smokeless powders. Single base powders are based on nitrocellulose alone and double base powders contain nitroglycerine in addition to nitrocellulose, adding to its energy. Both types have their advantages and are widely used in small arms ammunition, and both types are available to reloaders. At the time of this writing, Winchester/Olin and Alliant exclusively produce double-base powders, all VihtaVuori and most IMR powders are single-base (700X and 800X are the double-base IMR powders that I know of), and Accurate and Hodgdon offer several powders of each type.
Smokeless powder does not explode when unconfined, unlike black powder. In fact, technically, smokeless powder does not explode at all; it merely burns rapidly. Smokeless powders are classified as flammable solids. This rapid burning releases a huge volume of expanding gasses which, if confined in the chamber of a firearm, accelerate the bullet (or shot charge) down the barrel, producing a high velocity in a very short distance. Zero to Mach 2 in 26 inches for most centerfire rifle bullets, for example!
The burning rate of smokeless powders is varied and controlled in various ways. One is by the physical size of the grains, flakes, or spheres of powder. The larger these are the slower the powder burns. Naturally, the exact chemical composition of the powder also affects its burning rate.
A third method is to increase the surface area of the powder grains. The individual grains of many cylindrical powders, for example, are hollow rather than solid cylinders.
Another way is by the use of deterrent coatings to slow the burn rate. These coatings retard the initial ignition of the individual powder grains. They may also decrease the burn temperature, which reduces throat erosion in firearms.
Always remember that the burning rate of smokeless powders is not constant. It varies dramatically based on the degree of confinement. That is why a small cartridge, such as the .22 Hornet, requires a completely different powder than a large cartridge like the .300 Weatherby Magnum. Stick with the powders recommended in the major reloading manuals for specific caliber and bullet applications.
Graphite is used as a coating to facilitate powder handling, and it is this graphite coating that gives smokeless powder it typical gray color. Stabilizing agents are also added to modern powders to enhance storage life.
The exact chemical composition of the individual smokeless powders on the market is unimportant to shooters and reloaders. Nor does it matter whether they are single or double-base powders. What matters are their burning rates and their suitability for various specific applications.
Smokeless powders come in identifiable shapes. There are tiny cylinders ("cylindrical" or "extruded" powder) such as IMR 3031, flakes ("flake" powder) such as Alliant Red Dot, and spheres or flattened spheres ("ball" powder) such as Winchester 296. Flakes and cylinders can be either single or double-base, but all ball powders are double-base. Cylindrical powders, especially, can vary enormously in grain size.
U.S. made flake powders tend to be fast burning double-base powders for shotgun or pistol applications, although a few European flake powders are used in rifles. Cylindrical powders are usually single-base rifle powders, although there are exceptions. Ball powders can have a very wide range of burning rates and range from fast pistol powders to slow rifle powders.
Note that there are many powders of each type (flake, cylindrical and ball), and it is not possible to visually identify specific powders. Nor is it possible to visually identify the powders used in factory loads by pulling the bullet, noting the grain shape, and weighing the powder charge. Most factory loads use non-standard powders that are not available to reloaders. Often these are batches of powder that were intended to be a standard type but fell outside of the allowable production tolerances. The major ammo makers have the facilities to test the performance of these out of specification powders and develop loads accordingly.
In addition to being classified by shape, smokeless powders are generally grouped by application based on their burning rate and properties. There are handgun powders, shotgun powders, and rifle powders. However, there is considerable cross-over. Many shotgun powders are also useful pistol powders (and vice-versa), and some fast burning rifle powders perform well in magnum handgun cartridges.
Many of the popular reloading manuals include powder burning rate lists. These are interesting for general comparisons, but remember that they are approximate and the degree of confinement enormously influences the burning rate of all smokeless powders. A given powder may be "slow" burning in one cartridge and "fast" burning in another of different size. The powders recommended in the various reloading manuals are proven to be correct for their intended application.
Temperature also influences the burning rate of smokeless powders. Loads that are perfectly safe when tested in cool climates may develop unsafe pressure in very hot climates.
Heat is a problem in most of the prime African hunting areas, and helps to explain why so many of the famous British dangerous game cartridges use such big cases and yet are loaded to relatively low pressure. The maximum pressure of these cartridges is designed to remain safe even in the blazing African heat. Smaller cartridges loaded to higher pressure for equal or superior ballistic performance (compare the .416 Rem. Mag. to the .416 Rigby, for example) may experience a dramatic increase in operating pressure when very hot, leading to erratic performance and even stuck actions. Needless to say, this is not desirable when facing dangerous game! Anyone planning a hunt in very hot climates would do well to load their ammunition to moderate pressure levels. Reliable ammunition is far more important to a successful hunt than maximum velocity.
Powder should be stored in the proverbial cool, dry place. Never expose smokeless powder to direct sunlight. Prolonged exposure to heat above 90 degrees F can cause smokeless powder to deteriorate. According to the Hodgdon Powder Company, deteriorating powder usually has a noticeable acidic odor (not the usual solvent odors of alcohol, ether or acetone), and a red dust or sticky substance may form on the powder. This deterioration can ultimately result in spontaneous combustion. Obviously, powder must be stored far from any possible exposure to flame, electrical sparks and heat sources.
Leave smokeless powder in the container in which it was sold. Such containers are designed to come apart should the powder somehow ignite, preventing the build-up of dangerously high pressure. Remember, the more smokeless powder is confined, the more dangerous it is. If powder cans are placed in a cupboard or cabinet, make sure it has weak wall joints and doors that can be easily blown open. A powder fire is bad enough; you must prevent the build-up of pressure that could lead to what is, effectively, an explosion.
Smokeless powders, once ignited, will burn until they are completely consumed. They provide their own oxygen for combustion and cannot be extinguished by depriving them of atmospheric oxygen. Since it is intended to burn, a smokeless powder fire is difficult to fight.
Smokeless powder represents one of the great breakthroughs in the development of firearms. Treat it with respect. Use it wisely.
Copyright 2003 by Chuck Hawks. All rights reserved.