The Gun Digest Book of .22 Rimfire. James E. House

As you look at the rimfire section of the ammunition counter in a sporting goods store you will see stacks of boxes labeled 22 Long Rifle (LR), 22 Winchester Magnum Rimfire (WMR), and 17 Hornady Magnum Rimfire (HMR). If the store has a comprehensive line of ammunition, you may also see boxes of the new 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. As this is being written, another 17-caliber cartridge or two are being marketed or are under development.

The frame of the Smith & Wesson opened at the bottom and was hinged at the top.

The Smith & Wesson No. 1 First Issue was the first revolver chambered for the 22 Short black powder cartridge. Shown here is a No. 1, Second Issue model.

Pinfire cartridges were produced in several calibers including shotgun rounds.

If this list of approximately 10 cartridges makes it seem like there are many choices in rimfire calibers, look again. The 22 Short, Long, Long Rifle and the two CB rounds are all used in the 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. 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. In this chapter, we will provide a brief history of rimfire ammunition and a description of some of the most significant obsolete and current rimfire cartridges.

Cartridge Development

One 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. Some of the basic principles involved in cartridge performance will be described in Chapter 7.

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

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