Gunpowder for cartridges: composition and optimal quantity

Chemistry helps us understand how la is composed gunpowder of our cartridges. Knowing not only the composition, but also the optimal quantities, allows us to use the rifles in complete safety and reliability.

A bit of history. Black powder is also known as gunpowder and it is a substance which burns progressively. Having a low explosive power, gunpowder is considered the most harmless explosive there is, so it is even sold freely in the United States of America.

Its chemical composition is saltpetre, vegetable carbon and sulfur. Currently there is no certain information about its invention, but some historians are led to think that its origin can be traced back to China many centuries before Christ. Embracing this theory, it can be assumed that these mixtures would have been imported into Europe by the Arabs, during and after the Crusades in the Holy Land.

Over many centuries, the use of black powder or gunpowder for the production of firearms and cannons was hampered by the problem of creating metal barrels capable of withstanding the explosion. Improvements in metallurgy, over the years, allowed the creation of smaller weapons, with the creation of the musket. Subsequently, the gunpowder found more and more space in parallel with technological progress in the field of metallurgy and the war industry.
Coming to the present day, let's see what it is, how it is made and how what we now call gunpowder works.
Currently, gunpowder retains the same chemical composition, but in the pyrotechnic field silicone is added to it, which has a water-repellent action and protects the powder from humidity.

Many of the propellants that we all use today for cartridges are based on nitrocellulose (Ne), a flammable substance that is obtained by nitrating cellulose (the main component of wood) with nitric acid, in the presence of concentrated sulfuric acid. The nitrocellulose thus obtained has the appearance of a paste, which is unusable as it is insoluble and non-workable.

In order for it to be processed and used in weapons, it must be solubilized with alcohol and ether-based solvents in order to make it plastic and workable. After this treatment, it is transformed into threads or thin sheets, from which cylinders or flakes of various length and shape will be obtained, that is what will later end up in the dispensers.
Many propellants on the market carry the initials Ne, but they are almost never really such, since some chemical substances are used which are used to adapt their characteristics (mainly the combustion speed) to the specific use they are intended for. These substances consist of additives and due to their chemical composition not to be considered real explosives. In the composition of the current propellants a real explosive is often chosen, nitroglycerin, usually referred to as Ngl.

Ngl is obtained by nitrating glycerin, a very dense substance with a sweetish taste and is a very powerful explosive, but also excessively sensitive to shocks and heat, so that as such it cannot be used in firearms, but (also very to a limited extent) as a mine explosive. However, Ngl is used as a solvent for Ne, in order to modify the latter with the aim of obtaining a more stable and efficient launch explosive.

Double base propellants, i.e. those comprising mixtures in varying proportions of Ne and Ngl, offer many advantages, such as high density, greater power or energy content and finally greater stability.
The propellants thus conceived are divided into four main forms: cylinders, square or rhomboidal sheets, irregular rounded granules with a porous structure and disks. There is also another category of propellants, which has the appearance of small spheres called Ball Powder, or even Spherical Ball Powder, or more simply BP.
Launch explosives have a rather controlled burning rate, in order to make them burn at different rates from the beginning to the end of the grain combustion, with a gradual and not instantaneous gas evolution. When ignited, a grain of propellant burns and consumes itself from the surface towards the inside, with a reduction in surface and volume.

The combustion rate control system, still widely used today, is of a mechanical or structural type: by piercing the propellant grain along its entire length, its surface remains constant from start to finish, since the pierced grain burns both from the external surface towards the inside, and from the surface of the hole towards the outside.
One of the first types of propellant conceived in this way was solenite, an extruded double-base propellant produced in Italy for loading the cartridges of model 1891 rifles since the early twentieth century.

During the Second World War, another type of propellant was produced by Dupont De Nemours for the US Armed Forces, intended for cannons of various calibers, whose grains bore as many as 7 longitudinal perforations. This powder was produced in large quantities (thousands of tons), which remained unused with the end of the conflict, to the point that Olin-Winchester thinks of using them for the manufacture of the first Ball powders. By adding varying amounts of Ngl, Olin-Winchester obtained a compound which was reduced into spheres of varying sizes by immersing it and treating it with a special chemical compound. The Olin patent is still used today, obviously with the improvements made possible by modern industrial engineering, to produce today's BPs. The combustion of a propellant in perforated grains is defined as neutral (neutral burning rate), and although it represents a significant evolution compared to that of black powder, it is still not able to satisfy the needs of the most modern cartridges, in particular those ball for rifled weapons.

To meet these needs, the propellant is treated with deterrents or phlegmatizers, substances that slow down the initial combustion speed, forcing it to burn slowly at the beginning, and quickly towards the end. The additives used to control the combustion speed are defined as phlegmatizers or deterrents, they increase stability, while the lowering of the combustion temperature is obtained with the addition of coolants, usually mineral oils. The propellants thus obtained are called differentiated and progressive, (progressive burning rate), i.e. slow at the beginning and fast at the end.
All the propellants that are used today are of the progressive type.
There are also medium-progressive type propellants intended for magnum cartridges for shotguns, those for revolvers and cartridges for high intensity semi-automatic pistols.

Finally, the types intended for rifled rifles are all of high and very high progressivity.
It is important to remember that in any cartridge, using the same propellant, the dose must necessarily be decreased as the weight of the ball increases, but to obtain high speed and power even with heavy balls, it will be necessary to resort to the use of more progressive propellants. .