Ammunition

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Ammunition:

This means the cartridges that the guns shoot. Let’s get some definitions clear:

A round consists of:

  • The cartridge case
  • The primer
  • The propellant powder
  • The bullet (or in a shot cartridge, the wadding and the shot charge)



The Cartridge Case:

This serves to hold the assembled round together. On firing, the case expands to release the bullet or shot charge and to seal or obdurate the breech and prevent the propellant gases from escaping. Rimfire and centre-fire cartridges are normally made of brass, whilst shotgun cartridges are almost universally made of polythene tube, although rolled paper tube has been used for a very long time.

Shotgun cartridges are made in such vast numbers that prices are very competitive and few people bother to reload them. Rifle and pistol cartridges are another matter: they can be relatively expensive, and in some calibres are not widely available. For these reasons, many shooters save their fired cases and reload them. Reloaded ammunition can also be superior in quality to that available commercially.

Once the round has been fired, the spent case has to be extracted from the chamber, and ejected, or removed from the gun. For this reason, the case either has a rim (and so is a rimmed cartridge), or has an extractor groove cut around the base, and is termed rimless.

 

The Primer:

This is usually a small "cup" fitted into the base of the cartridge case. It contains a small quantity of a detonating substance, so that when struck with sufficient force by the firing pin it explodes. The high temperature gases of the detonation are fed through a flash hole in the base of the case, and ignite the main charge of the propellant powder.

.22 rimfire cartridges are different; they are made from thin brass, and are formed with a hollow rim. The have no separate primer: the priming compound is placed inside the hollow rim. On firing, the firing pin strikes the rim of the cartridge, crushing it against the breech face of the gun, and firing the round. Rimfire cartridges are limited to low pressure, low velocity rounds, because the have to use a thin case. When brass cartridges were first developed, the rimfire system was very popular, but today its use is limited to the .22 rimfire family of cartridges, and one odd ball: the 9mm Flobert shotgun cartridge. Rimfire cases cannot be reloaded, which is why the average small-bore range is usually ankle deep in empties!

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Propellant powder:

Prior to about 1880, there was only one propellant powder, black gunpowder. 'Black powder' is the famous mechanical mixture of saltpetre (potassium nitrate), sulphur and charcoal. Black powder is a low explosive; once ignited it burns almost instantaneously, generating large volumes of gases, plus lots of smoke and soot. Its burning rate remains unchanged inside a gun chamber. It is not a very good gun propellant because it generates lots of smoke; the combustion residues rapidly foul up the gun's bore, and because it cannot generate enough pressure rapidly enough to generate high velocities. Towards the end of the 19th century black powder cartridges reached their zenith, usually using huge cartridge cases to propel enormous lead slugs at low velocities.

Black powder is still in use today to load muzzle loading guns. Using it is messy, smelly, and great fun.

In about 1880, smokeless powders appeared on the scene, and being constantly improved, are still in use today. Smokeless powders are not explosives, they are propellants. When ignited in the open, they simply burn with a bright orange flame; but when ignited in a confined space, their burning rate increases rapidly as pressure increases. Hence they burn very rapidly in the gun chamber, but they never explode. By varying the chemistry, shape and surface treatments of the powders, it is possible to produce powders that have widely varying and progressive burning characteristics.

The basic ingredient of all smokeless powders is nitro-cellulose, which is made by reacting nitric and sulphuric acids with cellulose fibres. A powder that consists largely of nitro-cellulose is called single base, whilst those blended with a proportion of nitro glycerine are called double base.

Nitro, or smokeless powders contain much more energy than black powder, and allowed the development of all modern guns, especially the high velocity centre fire rifle. They burn cleanly, with little if any smoke, they do not foul bores, they are unlikely to explode, and they have predictable burning characteristics (unlike black powder, which being a mechanical mixture containing an organic component, never can). Best of all, they do not leave behind corrosive deposits like black powder does, so the gun generally needs very little cleaning after shooting. Because smokeless powders are not explosives, there are few controls needed on their purchase, unlike black powder, which requires an explosives licence to acquire and keep.

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Bullets:

These are the projectiles that actually make the scoring holes in the target. Originally, back in the muzzle loading days, all bullets were made of soft lead and were spherical. Lead is an ideal bullet material because it is soft, very dense (and thus heavy for its size) and is easily cast. Towards the end of the muzzle loading era, the conical bullet was developed as the science of aerodynamics was advanced; a long pointed bullet is much more aerodynamic than a round ball. With the advent of smokeless powders, chamber pressures and muzzle velocities were dramatically increased. Soft lead bullets are not suitable for high velocity nitro pistol and rifle cartridges, because lead is stripped off the bullet and left in the rifling grooves, destroying accuracy. The first route tried to solve this problem was to harden the lead by allowing it with tin, antimony and arsenic. This produces harder bullets that work quite well in pistol bullets (as we use in gallery rifles) and in .22 rimfires, but is still not good enough to make bullets for high velocity rifle loads. The ultimate solution is the jacketed bullet; in this, the bullet has a lead core, surrounded by a thin jacket of gilding metal (which is copper coated brass sheet). Development of jacketed bullets has continued to the present day, bullets that we use today being unthought of 25 years ago. We can thank modern computing power and CNC production machinery for this.

There is a downside to the modern high pressure, high velocity rifle cartridge: it wears rifle barrels out like lead bullets never will. Modern target rifles need to be rebarrelled on a regular basis, perhaps after as little as 5000 rounds, which might be only 2 or 3 seasons for an active shooter. Small-bore rifles and gallery rifles are unlikely to ever need rebarrelling as long as they shoot lead bullets.

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Wadding and shot:

In a shotgun cartridge the wadding separates the shot from the powder. When the gun is fired, the gases act on the wadding, like a piston, and drive the wadding and shot up and out of the barrel. The function of the wadding is to seal the gases in. Nowadays there are two types of wadding: the one-piece plastic wad, and the fibre wad. The one-piece plastic wad is the most common and effective, but can give rise to a litter problem, which has led to a revival in the popularity of the traditional fibre wad, which is biodegradable.

Shot is normally tiny spheres of lead, usually alloyed with small amounts of tin and antimony to harden it slightly. Shot is still mostly made by the traditional process of dropping molten lead through fine sieves down a high tower. On the way down, the droplets become spherical, and solidify. Because of concerns about lead in the environment, lead shot is banned in certain locations.

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