Take apart a modern metallic cartridge and you will find four primary components. The Bullet or Projectile, the brass case sometimes called a shell, a primer, and the propellent. Smokeless powder has completely taken over as the propellent of choice for all modern cartridges. However what is? What is it made of and how is it better then Black Powder?
Black Powder
Black powder is comprised of three primary elements. Sulfur, Charcoal, and Potassium Nitrate (Saltpeter), the development and use powder traces its history back to 9th Century China. It is largely credited as being the first chemical explosive developed. Black powder rien supreme for nearly 1000 years before it’s successor, Smokeless Powder was developed.
The ideal chemical makeup for Black Powder was well understood. In 1879 the French used the ratio of 75% Saltpeter, 12.5% Charcoal, and 12.5% Sulfur, British formulations were similar 75% Saltpeter, 15% Charcoal, and 10% Sulfur. Different formulations were developed for different uses. Rocket propellent used in British Rockets of the same time period used the ratios of 62.4% Saltpeter, 23.2% Charcoal, and 14.4% Sulfur.
By playing with the ratios of the three primary chemicals different burn rates could be establish. A rocket needs a long sustained burn to propel the rocket over a distance, while small arms need a much faster burn in order to burn all the propellent over the very short distance of the length of the barrel.
Burn rates could be further control by the size of the “Corning” in more conventional lingo, the size and geometry of the grain. Cannon powders can be found at 4-12 mesh (.187in to .066in) , and fast burning primer powder can be found at 40-100 Mesh (.016in to .0059in).
All things being equal a finer grain powder burns faster, primarily due to the amount of surface area exposed being greater than a coarse grain. As development of black powder reach its peak, there was more and more attention and develop of the geometry of the grain. This resulted in different shapes, such as hexagons or grains with perforations. Mainly used in large caliber guns.
There were several drawback with black powder. First, when it burns it creates a large amount of solids. Approximately 55%. This is the white smoke that is seen. During a battle the white smoke would cloud battlefields obscuring troop movements. A burst of white smoke was a dead giveaway for where a shot came from. The solids themselves would gum up the barrels, making bores tighter. The next shot would always be harder to load then the first.
Furthermore the solids were hygroscopic, meaning they readily absorbed moisture. If a black powder gun is left dirty, it is guaranteed to corrode.
The last black mark against black powder is the energy content is low. About 3 Megajoules per kilogram (~1.0 Million Foot Pounds per Pound). For comparison TNT has roughly 4.7 Megajoules per kilogram (1.5 Million Foot Pounds per Pound), and gasoline has 47.2 Megajoules per kilogram (15.7 Million Foot Pounds per Pound). When it’s mixed at an ideal stoichiometric ratio, the energy drops to 10.4 Megajoules Per Kilogram (3.4 Million Foot Pounds per Pound).
Modern Smokeless Powder may have as much as a 30% higher energy content. Slow burning powders such as N570 have as much as 3.9 Megajoules per Kilogram (~1.3 Million Foot Pounds per Pound).
Black Powder loads typically are low pressure, less than 25,000psi. Though when used improperly it can generate very high pressure. Like smokeless powder, black powder is considered a low explosive, meaning the flame front doesn’t not exceed the speed of sound. It is important to note that black powder burns at the same rate regardless if it is confined or unconfined, this is not true of Smokeless powder which burns faster when confined. Black Powder and Smokeless powder cannot be interchanged!
Development of Smokeless Powder
The development of Smokeless powder can be traced back to 1846 with the German Chemist Christian Friedrich Schönbein who developed nitrocellulose, known at the time as Gun Cotton. This composition was more powerful than Black Powder, and it was sold primarily as an explosive.
Around the same time in 1847 Nitroglycerin was first developed in a lab. Contrary to popular belief it was an Italian Chemist Ascanio Sobrero, not Alfred Nobel, who first nitrated glycerin. Alfred Nobel figure out how to take the unstable chemical and package it for use as an industrial explosive.
These two independent discoveries laid the foundation for what makes up the primary components of virtually all smokeless powders in use today. The development of a usable powder from these base chemicals took nearly 40 years from their initial discovery. The first commercially viable smokeless powder was invented by Paul Vieille and called Poudre B, short for Poudre Blanche, french for Powder White. This was developed for the French 8mm Lebel Rifle.
This first powder was nearly entirely comprised of Nitrocellulose, but forever changed the propellent world. The powder burned cleanly, giving off very little smoke, and resulted in higher muzzle velocities. Higher muzzle velocities are advantageous as the bullets follow a flatter trajectory, are less susceptible to winddrift, and increased the effective range. It didn’t take long for other European countries to develop their own formulations of this new Smokeless Powder.
In 1891 Alfred Nobel received a patent for Ballistite. This propellent used both Nitrocellulose and Nitroglycerin effectively creating the first Double Base powder. The British were unsatisfied with all of the propellants and commissioned a propellent of their own, Cordite, in 1891. This too was a double based powder at 58% Nitroglycerine, 37% Nitrocellulose, and 3% mineral jelly. Cordite was extruded into long strands, and can still sometimes be found pack in old military surplus World War 1 .303 British.
Cordite was an improvement over existing powders as it had a lower chamber pressure, but it held a higher pressure over a longer period. The combustion temperature was also lower, which reduced throat erosion and extended bore life. Since that time the variations of Smokeless powders have exploded.
Smokeless powder comes in all different forms, using Nitrocellulose as a base (Single Base Powders) to using a combination of Nitrocellulose and Nitroglycerin (Double Base). There does exist some powders that use one more constituent, Nitroguanidine, forming a Triple Base powder. Nitroguanidine is commonly used as a propellant in airbags, and in large bore artillery. One of the advantages of Nitroguanidine is that is burns as a lower temperature, this reduces throat erosion, desirable for large caliber expensive cannon barrels. However it is also hygroscopic, which can pose long term storage issues.
In 2015 a company called Stealth Gunpowder advertised a smokeless powder which utilized Nitroguanidine, however in researching for this write up it would appear their website is no longer active. The product never materialized.
Smokeless powder requires two things to burn efficiently, heat and pressure. Without enough heat the powder will not ignite. If it does ignite is may burn slow or “Smoulder” before suddenly going off. This creates a “Hangfire”, ignition can be delayed by a few milliseconds or as long as 30 seconds or more. Using the correct primer for a load, is important to provide enough heat to ignite the propellent.
Pressure is required as an accelerant. Smokeless powder burn faster the higher the pressure. Without pressure the powder will not burn completely or will burn very inefficiently. This can be demonstrated by burning the powder in open air. Black Powder will burn very rapidly. Smokeless powder will burn much slower, however if sand is placed on top of the powder to cover it, it will help contain some of the gases creating a little pressure which will help accelerate the burn.
The relation between temperature and pressure create a feedback loop of sorts. Typically the higher the temperature the faster the burn the higher the pressure. The higher the pressure the higher the temperature the faster the burn the higher the pressure. If not carefully controlled pressures using smokeless powder can quickly spike out of control.
This relationship between temperature and pressure holds true once the powder is burning. The start temperature of a propellent can determine how that propellent burns for example freezing propellets that are high in Nitroglycerin, such as Lil’Gun, can result in dangerous pressure spikes as Nitroglycerin burns faster the colder it is.
Next Generation Propellants
Smokeless propellants continue to be developed and improved as our understanding of chemical engineering and manufacturing controls continues to grow. As far as the industry is concerned developments in propellants are typically geared towards reducing flash signature, reducing copper fouling, and creating temperature stable propellants.
What is on the market today is miles ahead of the Cordite and the Poudre B of yesteryear. The difference is not the base chemicals as much as it is the geometry of the grain and the chemical additives that coat the grain. These additives can act a retardants which slow the burn of the grain, creating a harder to ignite but longer burning grain, or in the case of graphite, create lubricity preventing the clumping of the powder and allowing for uniform metering on loading equipment.
Grain geometry play a big role in the burn characteristics of modern smokeless powders. This is everything from the macroscopic shape of the grain to the microscopic fissures in a grain that create surface area. There can be some truly unique shapes, such as the donut shaped grain of Trail Boss, and the Cut Sheet flakes found in many Vectan pistol powders.