Development of Rimfire Ammunition

Development of Rimfire Ammunition


If the Rimfire section of the ammunition counter in a sporting goods store is well stocked, you will see stacks of boxes labeled .22 Long Rifle (LR), .22 Winchester Magnum Rimfire (WMR), .17 Hornady Magnum Rimfire (HMR), and .17 Winchester Super Magnum (WSM). If the store has a comprehensive line of ammunition, you may also see a few boxes of .17 Mach 2, .22 Short, .22 Long or perhaps those dinosaurs known as the .22 CB Short and .22 CB Long that live on for some reason. It is possible that you may also see a box or two of .22 Winchester Rim Fire (WRF), a cartridge that was introduced in 1890 along with the Winchester Model 90 pump rifle that was chambered for the cartridge.

If this list of approximately 10 cartridges makes it seem as if there are many choices in rimfire calibers, look again. The .22 Short, Long, Long Rifle and the two CB rounds may all be fired in a .22 LR chamber. The .22 WMR is a separate caliber, as are the .17 HMR and .17 Mach 2. We can ignore the .22 WRF for the moment, but it can be fired in a .22 WMR.

What we have is really a short list of rimfire cartridges, most of which can be used in firearms of one caliber, but as we shall see it has not always been so.

Cartridge development

We should not lose sight of the fact that developments in different areas of science and technology are interrelated. For example, it would not be possible to build a long-range rocket without developments in rocket fuel (which is a problem in chemical science). It was not possible to produce the atomic bomb until methods of enriching uranium were developed. The high performance of cartridges today is in great measure the result of improvements in propellants and metallurgy. A cartridge consists of a primer, propellant, projectile, and a case to contain these components. In order to ignite a propellant, some substance that explodes is needed.

The cause of the explosion is actually percussion (crushing the primer), which 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 is required for accuracy), it is necessary to have the same amount of explosive (primer) ignited in the same way for each shot and to have the same amount of propellant in each cartridge.

Flintlocks and cap locks

Early developments in muzzleloading firearms include ignition systems known as the flintlock and the cap lock, 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 could be easily ignited by the sparks produced when a piece of flint struck a piece of steel, which is 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 that 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 in turn 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.

From muzzleloading to metallic cartridges

Cap lock rifles of yesterday and today are relatively reliable devices. This author has fired many rounds through his muzzleloading Rimfire Rifles with only a few instances of misfiring or delayed firing (known as a hang fire). Loading a cap lock 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 muzzleloading 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.

Over time, 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 so it could ignite the powder charge. Attempts to solve that problem led to several early designs in metallic cartridge Ammunition.

Early designs in metallic cartridges

Black powder had been in general use in muzzleloading 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, whereas a coarse granulation designated ofFg is comparatively slow burning. Black powder used most often in rifles is FFg (medium) although FFFg (fine) is used in handguns or rifles of small caliber.

One of the early designs for a self-contained cartridge is known as the pin fire, and it dates from about 1830, when it was invented in Paris by Monsieur Casimir Le Facheux. 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 muzzleloader. With pin fire 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 pin fire left a lot to be desired. However, cartridges of this type were fairly popular in Europe and some shotguns employed this type of cartridge.

Pin fire cartridges were produced in several calibers, including shotgun rounds.

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 centerfire design rather than a true rimfire.

Teat fire cartridges were developed in the 1800s before rim fire cartridges were introduced.

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 very small cartridge known as the .22-caliber BB (bulleted breech) cap. Power was the result of the primer because 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 appears

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, which allowed the priming mixture to be contained in the rim.

The priming mixture was placed in the case while wet, and spinning the case caused the mixture to fill the void in 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, which was 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, which 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 3-4 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, and it became the precursor of the .22 Short.

Although it is 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 that could be fired in a small handgun! In modern times, small semiautomatic pistols chambered for the .22 Short have been produced for concealed carry and self-defense. Fired from a rifle, the 29-grain bullet from the .22 Short high velocity load has a velocity of approximately 1,095 ft/sec., whereas the 27-grain hollow point bullet has a velocity that is a slightly higher.

The four approaches to firing metallic cartridges are illustrated here. The cartridges illustrate (left to right) teat fire, pin fire, rimfire and centerfire types.

Introduced in 1887, the .22 Long Rifle (LR) is by far the most popular rimfire cartridge. However, another .22 rimfire cartridge appeared in the 30-year interval between the introduction of the Short and the Long Rifle cartridges. That cartridge, the .22 Long, was introduced in 1871 and made use of a 29-grain bullet propelled by a charge of five grains of black powder. As with other .22 rimfires, the .22 Long eventually became loaded with smokeless powder.

The current .22 Long cartridge has an advertised muzzle velocity that is about the same as that of the .22 Short. Any difference in power is more imagined than real, and there is no logical reason for the .22 Long to survive. Most of the Rimfire ammunition companies have ceased production of the .22 Long.

The .22 LR

When we come to the .22 LR, we arrive at a cartridge that is the most popular and widely used metallic cartridge that exists. It is used throughout the world for recreation, competition and hunting. The original load consisted of a 40-grain bullet and a five-grain charge of black powder.

Ammunition in .22 LR caliber is loaded in many parts of the world, and in some instances to the highest level of technical perfection. The accuracy capability built into a competition rifle chambered for the .22 LR is matched by several types of ammunition that are specifically designed for competition at the highest level. Such ammunition is a far cry from the old black powder loads with corrosive priming that appeared in the 1880s.

The .22 LR uses a bullet of 0.223-inch diameter that has a short section that is smaller in diameter (the heel), which fits inside the case. The lubricated portion of the bullet is outside the case.

Although the target shooter has special ammunition available, the hunter of small game and pests has not been left out. The .22 LR high speed solid uses a 40-grain bullet that has a muzzle velocity of approximately 1,235 ft/sec., whereas the 36-38-grain hollow points are about 40-50 ft/sec. faster.

The .22 LR is in many ways the most useful cartridge in existence. A rifle or handgun chambered for this round can be used for many purposes.

Editor’s Note: This article is an excerpt from Gun Digest Book of .22 Rimfire, 2nd Edition, by James E. House and Kathleen A. House


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