Black Powder XXV - Pellet Powder

In our last few posts, we saw some developments in compressed black powder technology, prismatic powders and pebble powders. In today's post, we will study another type of compressed powder called pellet powder, which was invented in the 19th century.

Pellet powder was a large grain powder designed to be used in larger guns. In our above example, each pellet is a formed cylinder of black powder about 1.25 inches in diameter with a hole in the center.

Sir John Anderson of Woolwich arsenal in England invented a machine in the 19th century for their manufacture, the details of which are below:

A machine for making pellet powder invented by Sir John Anderson. Click on the image to enlarge. Public domain image.

It consists of a disk of about 6 feet diameter (the pressing table) which revolves about one of the columns. The disk has teeth all around its circumference, which allows it to be rotated by means of a pinion and handle mechanism. The disk has four round metal plates placed symmetrically, about 2 inches thick and 1.5 feet in diameter. In each metal plate are drilled about 200 cylindrical holes of about 5/8 inch diameter. Above each plate is a movable covering-plate which can be pressed tightly against it, and into each of these 200 holes a small plunger enters, which goes through the bottom part of the disk and can be lifted from below by a hydraulic press.

Two opposite plates are always pressed at the same time. As soon as the movable plates are lifted, the molds are filled with meal powder, the plates are cleaned and excess powder wiped off, and the movable plates lowered and fixed so that they close the holes on the top. Then the plungers are pressed into the molds, causing the layer of powder to be compressed to 5/8 inches in height. After this, the movable plates are lifted and the plungers are pushed further into the holes, thereby pushing the formed pellets out of the mold holes.

Click on the image to enlarge. Public domain image.

After the pellets are pushed out, the disk is then rotated for a quarter turn and the pellets are taken off the two mold-plates. Meanwhile the same operation is then carried out with the other two plates.

The pressure applied to the powder by this machine is about 0.5 tons per square inch. The pellet formed is shaped like a cylinder with one or both bases having a hollow in the middle in the shape of a blunt cone. The size of the pellets made by this machine are 5/8 inch diameter, 5/8 inch height and depth of the hole is 1/4 inch and each pellet weighs about 100 grains.

In America, the Du Pont powder company made a hexagonal pressed pellet powder, which looks like two truncated hexagonal pyramids connected by a cylindrical layer of powder.

Du Pont Powder. Public domain image.

This powder was made by the following process: A lower plate in which a number of pyramidal holes were cut was covered with powder and a second similar plate was laid over it and then pressure was applied. Depending on the thickness of the layer of powder, the cylindrical part connecting the two pyramidal halves will be thicker or thinner. After pressing, the cake is broken, this causing the grains to break off on the edges of the cylindrical part.

In Italy, they made compressed pellets in cubical form, sold under the brand name "Fossano Powder", because it was first manufactured in a gunpowder factory at the town of Fossano in northern Italy. Fossano powder is a type of "Progressive Powder" and was invented by Colonel Quaglia (the factory director) and his assistant, Captain de Maria.

Fossano Powder. Public domain image.

The manufacture of Fossano powder was done in multiple stages. In the beginning stage, meal powder was pressed into cakes of density about 1.79. Each cake was then broken up into irregular grains of about 1/8 to 1/4 inch in thickness. Then grains were then mixed again with a certain quantity of meal powder and then pressed into cakes again, with a density of 1.776. This second cake was then broken up into cubes. Therefore, each cube would be composed of powder pieces of higher density enclosed in a powder material of lower density, sort of like raisins inside a plum-pudding. The idea behind this was that due to the differing densities of powder, more gas would be produced after the powder has been partially burnt, than at the start of ignition of the powder, leading to the 'progressiveness' of the explosion (which is why it is called a "progressive powder"). This allows the pressure on the projectile to be maintained during its course in the bore and possibly increased while it is moving away.

Pellet powders burn slower than other ordinary large grained powders due to their larger grain sizes and is therefore less violent in action. Experiments in England showed that these could produce muzzle velocity greater than ordinary large-grained powder with peak pressure hitting about half that of large-grained powder.

Pellets are still available today for black powder enthusiasts:

Pyrodex 50/50 grain pellets/

Click on the image to enlarge.

Click on the image to enlarge

The above images show modern pellets available today in many sporting goods stores. However, these are made of black powder substitute, not original black powder. Black powder substitute is less sensitive to ignition than real black powder and is more energetic.

Black Powder XXII - Compressed Powder

In today's post, we will look at a form of powder that was used during the Civil War, called compressed powder. The origin of this powder has to do with larger guns rather than firearms, but is still an interesting point of study, since it leads down to prismatic and pebble powders later down the line.

General Thomas J. Rodman. Public domain image.

The first breakthrough into compressed powders was due to a career US Army officer named Thomas Jackson Rodman. He was an inventive man with an interest in artillery, and early in his career, he was appointed as a brevet second lieutenant in the US Army Ordnance Department, where he started working at improving cannons.

At around 1856, he noted that ordinary service powder could not be used in larger guns, because the initial gas pressure developed was sometimes high enough to cause the gun to be destroyed. The range of the gun was also reduced. The reasons are as follows:

If a fine grained powder is used for a large gun, a large portion of it is burned at the moment of ignition, due to its larger surface area (remember that black powder is surface burning and the larger the outer surface area of the powder, the faster it burns). Therefore, this causes a very high maximum pressure to be generated at the beginning and then tapers off as the rest of the powder burns, which leads to a lower average force, compared to the initial force. In fact, the initial pressure may be high enough to cause the cannon to explode with disastrous results. Therefore, the rate of combustion of the gunpowder had to be reduced somehow.

Rodman found from his experiments that he could considerably reduce this initial pressure in the gun by using disks of compressed powder, perforated by holes. The disks were made of a diameter equal to that of the bore of the cannon and between 1 and 2 inches in thickness and perforated with a number of holes.

With this type of powder, the surface area of the powder is smaller initially and only develops enough pressure to overcome the inertia of the cannon ball. Consequently, the projectile properly engages the rifling and gets pushed out with a regular motion, which is very important because accuracy depends on uniform movement of the projectile in the barrel

Surface area comparison of ordinary powder (green) vs. Rodman's compressed powder (red cylinder). Click on the image to enlarge. Public domain image.

As the powder burns more, the surface area exposed increases due to the constant enlargement of the holes bored through the compressed powder. Due to the constant increase of the area of the burning surface, this causes a corresponding constant increase in the rate of production of the burning gases. This results in a longer and more consistent burn time inside the bore of the barrel. Therefore, the average pressure generated is higher and this increases the range of the gun significantly, without making the pressure rise to dangerous levels initially.

Rodman first published his discoveries in a scientific paper in 1861 ("Properties of Metals for Cannon and Qualities of Cannon Powder") and his ideas were put into practice in the Civil War. His special compressed powder was produced under the name "mammoth powder" and other inventors also benefited from his breakthrough, as we'll see in our next few posts.

As a result of his work, Rodman was promoted to brevet brigadier general at the end of the Civil War. He remained in the military for the rest of his life, being promoted to the permanent rank of lieutenant colonel in the US Army. Incidentally, in 1865, he was sent to Rock Island, Illinois and put in charge of supervising the construction of a new military facility, which became the Rock Island Arsenal, which still exists and is one of the largest government-owned weapons manufacturing factories in the United States.