Shrapnel Shell

Background

There has always been a high demand among military strategists for economical means of killing enemy soldiers. Economy is required not so much to save money, but to allow outnumbered soldiers the opportunity to win battles. Prior to the advent of high-powered rifles, soldiers in opposite armies would form ranks preparing for battle in clear sight of each other. However, artillery was generally ineffective against troop formations at long range until late in the eighteenth century.

History

Lieutenant Henry Shrapnel of the British Royal Artillery solved the distance problem in 1784. Shrapnel's contribution was to pack musket balls into a container that could survive being fired out of a cannon. The round case shot was simply a hollow cannon ball that contained musket balls in a gunpowder matrix. A time fuse made out of paper wrapped around more gunpowder, rather like a firecracker fuse, was inserted into the cannon ball and lit. The cannon ball was then fired at the enemy troops. If the cannoneer timed the flight of the ball properly, the ball would explode just as it arrived above the enemy troops, releasing the musket balls.

Shrapnel was largely ignored. However, by 1803 he was a captain and was allowed to demonstrate his invention for the British Army. Shrapnel's invention was instantly recognized to be one of the super weapons of the day, evidenced by the speed with which the British Army put it into production—only two months after Shrapnel first demonstrated it.

The Shrapnel shell was first used in combat in 1804 in Surinam on the north coast of South America against Dutch settlers. The Dutch surrendered after receiving their second round of Shrapnel shells. Shrapnel was promoted to lieutenant colonel in 1804, less than a year after making major.

There were numerous improvements made in the Shrapnel shell between the final defeat of Napoleon and the phasing out of Shrapnel shells during World War I. Shrapnel's round ball evolved into an artillery shell that looked very much like a modern shell and was manufactured in much the same way. It also performed the same function: the delivery of lead balls over long distances in large quantities at high velocities.

Raw Materials

The shell was made out of forged carbon steel. The purpose of the shell was simply to contain the lead balls and funnel them downward toward the target. The shell was not intended to explode into fragments. Cartridge cases were almost always made out of brass. Brass was used because it expands during firing. As the cartridge case expanded, it sealed the gun barrel in a process called obturation. Obturation provides greater thrust to the projectile and also protects the artillerymen against backfire. The Shrapnel balls were made out of lead. Lead was also used in bullets, as it is both heavy and soft. Because lead is soft, it gives up more of its energy to the target (flesh) rather than passing through the target and expending its energy against the landscape. The rotating band was made out of an alloy known as gilding metal, which consists of 90% copper and 10% zinc. The rotating band provided forward obturation (so that none of the propelling charge would blast by the shell in the gun barrel and be wasted) and also imparted a spin on the shell as it moved up the barrel. Spin was induced in the shell by the barrel's rifling—the spiral ridges cut in the barrels of many types of guns. Just as a football that does not spiral will rotate end over end and not go where it was intended, an artillery shell that is not spin-stabilized might end up anywhere.

The base charge for most artillery shells was usually a combination of nitrocellulose and nitroglycerine. Common primer materials used to ignite the base charge include mercury fulminate, lead azide, lead styphnate, and nitromannite. These chemicals are extremely shock-sensitive and will explode when hit sharply. The artillery primer would ignite a booster charge of gunpowder that was inserted into a perforated hollow spike that penetrated most of the length of the base charge. The purpose of the booster charge was to ignite as much of the base charge as possible at the same time. The fuse in Shrapnel shells consisted of a brass plug that screwed into the top of the shell. The brass plug contained hollow channels that contained gunpowder, and the fuse could be adjusted to provide a given delay in firing. The fuses were initiated by the force of the initial acceleration of the shell as it left the cannon barrel. Modern artillery fuses are almost always solid state electronic timers or proximity fuses.

Design

The design of an artillery shell involved determining the purpose of the shell and then matching the purpose to the cannon (modern artillery pieces are mainly howitzers, the distinction being that howitzers fire along parabolic arcs over the horizon whereas cannons fire along a line of sight) from which the shell will be fired. The designer had the specifications for the cannon, and thus knew that the shell must have a certain diameter and could only generate a certain amount of thrust without damaging the cannon. The shell had to be simple enough to allow for rapid firing but intrinsically safe so that a shell dropped in the heat of battle would not explode and kill the wrong people. The fuses of Shrapnel shells were precisely designed so that the shell would explode at exactly the right moment. A Shrapnel shell that went off too far from the target would do little damage, while a shell that went off after hitting the ground would do no damage.

The main components of a Shrapnel shell were the shell itself, the cartridge case, the lead balls, a base charge to propel the shell to its target, a charge to expel the lead balls from the shell, a primer charge to set off the base charge, and a fuse to set off the expelling charge. Other miscellaneous components included a rosin mixture to hold the lead balls in place and which produced smoke to assist the artillery spotters, a steel push plate between the lead balls and the expelling charge, a rotating band on the base of the shell to spin the shell as it moved up the gun barrel, and a nose cone to reduce aerodynamic resistance of the shell.

The Manufacturing
Process

The shell

• 1 First, the Shrapnel shell was forged. In forging, a cylinder of carbon steel is heated almost to the melting point and then manually beaten into the rough shape of the final product. The rough forging was then machined to the final shape.
• 2 The cross-section of an artillery shell is slightly smaller than the inside diameter of the cannon barrel except for two locations: the top of the cylindrical portion of the shell and the rotating band. The top band is known as a bourrelet. The bourrelet and rotating band provide a very close tolerance (only a few thousandths of an inch) between the shell and the cannon barrel. A groove is milled into the base of the shell into which the rotating band is pressed. For a Shrapnel shell, the center of the shell is then drilled out to hold the lead balls.
• 3 Gunpowder was used to expel the lead balls. One to two ounces (28-56 g) of gunpowder was inserted into the shell under carefully controlled conditions to prevent accidental detonation. A cloth disk was inserted into the shell to separate the base charge from the lead balls. A metal diaphragm (push plate) was then placed on top of the cloth separator. The push plate and cloth separator contained a hole into which a steel flash tube was press-fitted prior to insertion.
  

  A cut-away of a shrapnel shell.
  In press fits, the part to be inserted has a slightly smaller diameter than the hole into which it is forced. Large forces are necessary to press the part into its hole, which provides a tight fit that will not come loose. The purpose of the flash tube was to transmit the flame from the primer charge in the fuse at the nose of the shell down to the gunpowder in the base of the shell.

Lead balls

• 4 The lead balls were manufactured by pouring molten lead through a steel screen. As the molten lead flowed through the screen, it formed spherical droplets, the diameter of which were controlled by the size of the openings in the screen. The molten lead droplets fell against a counter-current of forced air that solidified the molten lead, and then into running water, which hardened them further. Typical Shrapnel balls were about 0.51 in (13 mm) in diameter, though larger balls were sometimes included to kill horses.
• 5 The lead balls were mixed with pine rosin (the substance left over after turpentine is distilled out of pine sap) and poured into the shell. The rosin was allowed to harden in the shell. The purpose of the rosin was to prevent the lead balls from rattling around in the shell during flight, which might have caused premature ignition of the gunpowder. The rosin also provided smoke so that artillery spotters could determine if the shells were being timed correctly to explode above their targets.

The Fuse

• 6 The Shrapnel shell fuse was a complex mechanical/chemical device machined out of brass and threaded to fit the shell. Its complicated design and tiny components made for difficult assembly, and a large portion of the munitions industry was devoted to turning out these parts. Brass was chosen as it is non-sparking (if struck, it does not produce sparks that may ignite the powder train and cause premature explosions). The fuse consisted of two different primer charges separated by two channels containing gunpowder. The connection between the two channels (and thus the speed of ignition) could be adjusted by rotating the bottom portion of the fuse. The first primer was activated by the acceleration of the shell as it was fired. The acceleration drove a plunger against a stiff spring into a gliding metal or aluminum cup containing the primer, which exploded on contact.

The cartridge case

• 7 The cartridge case was stamped out of brass. Stamping involves placing a flat piece of metal between dies and progressively beating it into the desired form. In the case of cartridge cases, multiple anvils and hammers were used to obtain the final shape.
• 8 A separate primer was required to set off the base charge in the cartridge case. The primer was contained in a gilding metal or aluminum cup that would be contacted by a steel anvil. The anvil would be pushed into the primer by the howitzer's firing pin. The primer ignited a booster charge of gunpowder that then ignited the base charge. The primer and booster charge were contained in a hollow brass spike that was pressed into a hole in the base of the cartridge case.
• 9 Final assembly of the shell was accomplished by crimping. A groove semi-circular in cross section is cut into the shell. The cartridge case is fitted over the groove and the entire diameter around the groove is compressed until the brass cartridge case actually flows into the groove and forms a tight bond.

Quality Control

Quality control is extremely important in ammunition manufacturing as faulty ammunition can kill valuable soldiers. All artillery shells were manufactured in lots of specified sizes, usually 2,000-5,000 pieces per lot. The lot number was painted onto artillery shells so that the shells could be tracked down if problems with the lot cropped up later. A certain percentage of shell components were measured to verify that the parts were the correct size. Destructive testing was performed on representative samples to assure that metal components had the proper strength and that chemical components burned at the proper rate. Fuses were tested for waterproofing. Rotating bands were torn off shells to ensure that they had sufficient strength to withstand firing.

Once it was determined that the shells had been manufactured according to design, the shells were then field tested to determine whether the design had produced a shell that behaved in a predictable fashion. Some shells were deliberately overloaded with base charge and fired to ensure that they would not destroy the gun. Shells with inert fuses were fired, and then recovered, to assess whether the force of the firing would have set off the fuse prematurely. Shells were filled with sand and fired to assess how well the shell held together during flight. And a certain number of shells were fired to assure that the base charges would send the shells where the artillery operators intended them to go.

Byproducts/Waste

The major wastes generated by the production of artillery shells were produced during testing of the shells and the training of artillery operators. There are currently large sections of the United States that will never be able to be used because of the presence of artillery shells that were fired but did not go off. During actual production, the largest waste stream consists of cutting fluids and metal chips produced during machining.

The Future

Shrapnel shells were rendered obsolete during the first world war. They proved to be ineffective against troops protected by trenches, could not clear barbed wire entanglements, and were proven difficult to set so that the shells exploded at the proper height above the enemy troops. The Shrapnel shell was superseded by the high-explosive fragmentation shell, in which the shell casing was filled with an explosive that fragmented into hundreds of deadly pieces upon detonation. The latest technology for killing enemy troops at a distance is the Improved Conventional Munition, or ICM. The ICM is more similar to a Shrapnel shell than a fragmentation shell. The difference is that rather than spilling out simple metal balls, it spits out hand grenades, land mines, or anti-tank bombs. It is inevitable that the ICM will someday be superannuated by something even more efficient and tailored to overcome new defense strategies.