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The four approaches to firing metallic cartridges are illustrated here. The cartridges illustrate (left to right) teatfire, pinfire, rimfire, and centerfire types.
Teat fire cartridges were developed in the 1800s before rim fire cartridges were introduced.
A cartridge consists of a primer, propellant, projectile, and a case for these components. In order to ignite a propellant, some substance that explodes is needed. The cause of the explosion is actually percussion (crushing) that is the result of a spring-loaded striker (hammer or firing pin) changing positions at the time of firing. In order to have shot-to-shot uniformity (which results in accuracy), it is necessary to have the same amount of explosive (primer) ignited in the same way for each shot and have the same amount of propellant in each cartridge.
Early developments in muzzle-loading firearms included the flintlock and the caplock, which used a percussion cap. In the flintlock, the primer consisted of a small amount of fast-burning black powder of fine granulation (FFFFg) that was ignited by the sparks produced when a piece of flint struck a piece of steel known as the frizzen. The priming charge was held in the flash pan, which had a hole that led downward into the barrel where the main propellant charge was held. The gas resulting from the burning powder in the main charge provided the driving force to move the bullet down the bore.
As firearm technology developed, so did the chemistry of explosives. It was discovered that mercury fulminate exploded violently when it was struck. Therefore, percussion caps were produced which consisted of a small amount of mercury fulminate contained in a small copper cup that fitted over a hollow nipple. When the hammer fell and struck the cap, the mercury fulminate in the percussion cap exploded which ignited the powder charge as fire was directed from the primer into the barrel breech. The percussion cap was introduced in the early 1800s, and its use in muzzle loading rifles continues to the present time.
Caplock rifles of yesterday and today are relatively reliable devices. This author has fired many rounds through his muzzle loading rifles with only a few instances of misfiring or delayed firing (known as a hang fire). Loading a caplock rifle is a slow process because the powder charge must be measured and poured into the barrel and a projectile loaded on top of the charge. The process is slightly faster if the projectile is a “bullet” rather than a lead ball that is used with a lubricated cloth patch. New developments in muzzle loading make use of propellant that is compressed into pellets of known weight. One or more of these pellets can be dropped down the barrel and projectile loaded on this charge. It became apparent that producing a single unit containing the primer, propellant, and projectile that could be loaded in one operation would be a great convenience. That is exactly the impetus that led to the development of so-called metallic cartridges. However, there still remained the problem of where to place the primer in the cartridge and how to cause it to explode reliably to ignite the powder charge. Attempts to solve that problem led to several early designs in metallic cartridge ammunition.
Black powder had been in general use in muzzle loading firearms for many years so it was the propellant utilized in early metallic cartridges. Black powder consists of a mixture of potassium nitrate (saltpeter), charcoal (carbon), and sulfur in the approximate percentages 75, 15, and 10, respectively. Burning rate of the propellant, which is designated by an “F” system, is controlled by the particle size. A granulation known as FFFFg (very fine, often referred to as “4F”) is a very fast-burning form while a coarse granulation designated as Fg is comparatively slow burning. Black powder used most often in rifles is FFg (medium) while FFFg (fine) is used in handguns or rifles of small caliber.
The 41 Swiss (left) and 22 Short (right) illustrate the range of cartridges that were eventually produced in rimfire calibers.
One of the early designs for a self-contained cartridge is known as the pinfire, and it dates from about 1830 when Monsieur Casimir Le Facheux invented it in Paris. The cartridge contained a bullet, propellant (black powder), and a primer. However, the blow of the hammer was transmitted to the primer by means of a pin that stuck out of the side of the case at the rear. This meant that the cartridge had to be oriented in the chamber in such a way that the hammer would strike the pin to push it into the case to crush the primer. Although placing the cartridges in the firearm in the correct orientation made loading slow by today’s standards, it was still rapid compared to loading a muzzle-loader. With pinfire cartridges, there was also the possibility that the protruding pin could be struck accidentally which could force it into the case causing the cartridge to fire. From the standpoint of safety, the pinfire left a lot to be desired. However, cartridges of this type were fairly popular in Europe and some shotguns employed this type of cartridge.
Another cartridge design consisted of a closed tube that contained the bullet and propellant with the primer being contained in a small protruding portion at the rear end of the tube. This type of cartridge, known as the Moore teat fire, was loaded into the front of the cylinder of a revolver with the teat at the rear where it could be struck by the hammer. The front end of the cartridge was flared to form a retaining flange that fit against the front of the cylinder. Cartridges of this design were produced in the mid-1800s. Because the protrusion that held the primer was located in the center of the cartridge head, it was actually a center fire design rather than a true rim fire.
Each of the early cartridge designs described above contained a primer that was sensitive to shock. Subsequent designs would also rely on shock or percussion to cause the primer to explode, but the primer would be located differently in the cartridge. In 1845, a man named Louis N. Flobert in France loaded a round ball in a percussion cap and produced a small cartridge known as the 22 caliber BB (bulleted breech) cap. Power was the result of the primer since no powder was used. Some American versions of this cartridge employed a conical bullet (hence these were known as CB caps) that was loaded over a small powder charge. In 1851 at an exhibition in London, Horace Smith and Daniel B. Wesson became convinced that this cartridge design could be refined.
The rimfire cartridge was developed by producing a cartridge case with a flange or rim of larger diameter than the body by folding the rear of the case over on itself. The rim was hollow and allowed the priming mixture to be contained within it. The priming mixture was placed in the case while wet and spinning the case caused the mixture to fill the hollow rim. When the primer was dried, it then became sensitive to shock. Crushing the rim by a forward blow of the firing pin caused the primer contained within it to explode which in turn ignited the powder charge.
A short, self-contained 22 caliber cartridge called the Number One Cartridge (essentially identical to the 22 Short of today except for primer and propellant) was introduced in 1854 by Smith & Wesson for use in a small revolver. The revolver was designated as the Smith & Wesson Model 1 First Issue produced from 1857 to 1860. It was followed by the Model 1 Second Issue that was produced from 1860 to 1868 and the Third Issue from 1868-1881. All issues of the Model 1 had a hinge that connected the barrel to the top of the frame at the front end. It was opened by means of a latch at the bottom of the front edge of the frame that allowed the barrel to be tipped up so that the cylinder could be removed for loading and unloading. The cartridge employed a 29-grain bullet that was propelled by 3 to 4 grains of black powder contained in a case that was slightly longer than that of the BB cap. A patent was granted on August 8, 1854 for the rimfire cartridge that was the precursor of the 22 Short. While certainly no powerhouse, the 22 Short has been used as a target load for many years in firearms designed specifically for that cartridge. As strange as it may seem, the 22 Short was originally viewed as a self-defense load! In modern times, small semiautomatic pistols chambered for the 22 Short have been produced for concealed carry and self-defense. The 29-grain bullet from the 22 Short high-velocity load has a velocity of approximately 1,095 ft/sec
