October 19, 2021
When I wrote about muzzle flash recently, I extensively referenced Tenney L. Davis’s classic textbook, The Chemistry of Powder and Explosives. It has been helpful in my understanding of propellant evolution and is a key source of historical information. Where Davis lacked information, I turned to Philip B. Sharpe’s Complete Guide to Handloading (Third Edition, 1953), which gives a superb and detailed account of propellant development and history, including actual component ratios taken from U.S. and foreign patents.
The development of nitroglycerine (NG) in Italy and nitrocellulose (NC) in Germany happened in 1846. We can trace our current propellant materials to those two breakthroughs. Treatment with nitric acid “supercharges” organic materials that contain stored energy; proper nitration enables the release of much more of that energy than normal burning.
Nitrating plant fiber—usually wood chips or cotton byproducts—to nitrocellulose also led to the discovery that certain solvents could soften it, resulting in a sticky, moldable mass. That led to the first recognized plastics like celluloid that replaced natural shell and bone for many household items. (Yes, a pocket comb of that period could double as a fire-starter in an emergency.)
If we had the two primary ingredients used in smokeless propellants in 1846, why did it take until the 1900s for them to take over the job of pushing bullets? The answer is control. These materials had great potential, but like keeping a pet velociraptor in the laundry room, they were difficult to contain. The real achievements were in developing that control.
Control fell largely into two categories: making the manufacturing process safe and repeatable and developing ways to allow softening of NC for shaping into granules (and, later, adding chemical treatment to control the rate of energy release).
The first task must have been fraught with hazard because Sharpe’s history of propellant evolution seems to include the phrase “plant blew up” in every third paragraph!
Solvents used to soften nitrocellulose for processing into granules are called plasticizers, and two types ultimately emerged. Those whose nitrocellulose was plasticized in an alcohol/ether cocktail became our “single-base” propellants; the solvents contribute very little energy. Those where nitroglycerin was the plasticizer became our “double-base” propellants because the NG contributes significant energy. Fully plasticized and reformed NC materials as used in propellant manufacture today were called “colloidal nitrocellulose” as far back as 1870.
Yet there were still contemporary propellants lacking NC/NG components in use while the development of modern energetic materials was underway. Some saw considerable use even in military settings.
During the American Civil War, a product called “white powder” eliminated charcoal from blackpowder. It added another high-oxygen potassium compound to boost the traditional potassium nitrate oxidizer. Apparently, the remaining sulfur in the presence of two very energetic oxidizers was quick to hydrolyze to sulfurous acid. White powder proved much more corrosive to typical low-grade steels than blackpowder and failed to thrive past the conflict.
A formula that saw military use in Germany and Austria was ammonpulver, German for “ammonia powder.” Patented in 1885, it lacked the sulfur from the traditional blackpowder mix, eliminating the “bad night of beans” odor of traditional blackpowder and substantially reducing its corrosive potential. This also had a second oxidizer, ammonium nitrate, to supplement the potassium nitrate (“saltpeter”), greatly reducing the smoke from the charcoal fuel.
Ammonpulver and its variants also demonstrated reduced flash compared to traditional blackpowders. The big issue was thirst; it absorbed and held moisture like a camel. Thus, it was more often applied as an artillery propellant than one for small arms. Semi-fixed artillery ammo had the charge preloaded in a metal cartridge case that could be effective sealed. On the other hand, rifle cartridges of the era could spend a lot of time at the bottom of a soggy trench or foxhole with a cold, wet infantryman. Nevertheless, it was used as late as World War I.
The transitional propellants that seemed the most obvious candidates were the simplest yet, by comparison, took the longest to see commercial use. They are essentially blackpowders spiked with nitrocellulose, broadly classed as “semi-smokeless” propellants.
Sharpe shows numerous citations of “wood powders” that blended wood-based nitrocellulose with the normal components of blackpowder. Variants existed as early as 1870 in the United States. The two most successful of these were King’s Semi-Smokeless and DuPont’s Lesmok.
Often these are cited as being blends of blackpowder and true smokeless propellants. However, Sharpe’s information, taken from the King’s 1899 patent, says King’s propellant used 20 percent “nitrated wood cellulose,” the remainder being the raw materials of conventional blackpowder. “Nitrated wood cellulose” implies an energetic material that has not finished production into colloidal nitrocellulose and would be much cheaper then. All he says for Lesmok is that it was “similar.”
Lesmok appeared a bit after King’s product. Both King’s Semi-Smokeless and DuPont’s Lesmok powders were loaded by major U.S. ammomakers starting before World War I. Some was used in .32-caliber revolver cartridges, but most went to .22 rimfire ammo, often even “target” ammo where it persisted far beyond what our modern minds can grasp. Winchester loaded the last lots of .22 rimfire target ammo with Lesmok in 1947!
These propellants reduced powder fouling significantly in tiny bores, but because they are roughly 80 percent blackpowder, they remain corrosive. Firearms required the same cleaning as those fired with regular blackpowder. Still, Lesmok must have shown some serious redeeming qualities if semi-smokeless target loads survived nearly a half-century!