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Cartridge (weaponry)

From Academic Kids

Rimmed, centerfire .303 in cartridge from WWII.
Rimmed, centerfire .303 in cartridge from WWII.

A cartridge or round packages the bullet, gunpowder and primer into a single metallic case precisely made to fit the firing chamber of a firearm. The primer is a small charge of impact-sensitive chemical that may be located at the center of the case head (centerfire ammunition) or at its rim (rimfire ammunition). Electrically-fired cartridges have also been made; see below. A cartridge without a bullet is called a blank.

Contents

Design

Missing image
Cartridge_30-06.png
.30-06 Springfield cartridge specifications. This is a rimless cartridge case. Measurements are in inches

The cartridge seals a firing chamber in all directions except down the bore. A firing pin strikes the primer, igniting it. The spark from the primer ignites the powder. Burning gases from the powder expand the case to seal against the chamber wall. The projectile is then pushed in the direction that releases this pressure, down the barrel. After the projectile leaves the barrel the pressure is released and the cartridge case is pulled out of the chamber.

Critical specifications include its caliber, bullet weight, expected velocity, maximum pressure, headspace, overall length and primer type. The diameter of a bullet is measured either as a decimal fraction of an inch, or in millimeters. The length of a cartridge case may also be designated in millimeters. Where two numbers are together, the first is the diameter, and the second is the cartridge length, e.g. the 7.62 x 51 mm has a diameter of 7.62 mm and an overall length of 51 mm.

Most high-powered guns have relatively small bullets moving at high speeds. This is because bullet energy increases proportionately to bullet weight and as the square of velocity. Therefore, a bullet going twice as fast has four times the energy (see physics of firearms). Bullet speeds are now limited by starting bore pressures, which in turn are limited by the strength of materials and the weight of gun people are willing to carry. Larger cartridges have more powder, and usually higher velocities.

The lethality of pistol ammunition is not limited by the ammunition, but by the accuracy and doctrine of the shooter. Rounds with these energies have insufficient momentum to knock people down (the recoil would break wrists), and move too slowly to cause significant hydrostatic shock.

Centerfire

Of the hundreds of different designs and developments that occurred, essentially only two basic differences remain. All current (civilian) firearms are either rimfire or centerfire. The military is still trying to perfect electrical firing, which does away with the primer.

Centerfire uses a centrally located primer, which, in most cartridges used by civilians, can be replaced, so that the expensive brass cartridge cases can be reused. This is called Boxer primed. The military uses a very similar system, called Berdan priming, which is fractionally cheaper, but prevents the case from being easily re-used. With care, they can be reloaded, however, and are easier for guerillas/freedom fighters to reload, as the new "primer" can be as simple as a bit of tin can and a match head, unlike the multi-stage process required for making a boxer primer.

Rimfire

Rimfire, of which only the popular .22 LR remains in common use, was a popular solution before the centerfire design was fully perfected. It can only be used for fairly low powered cartridges, as the case has to be soft enough to be deformed by the firing pin, which detonates the priming compound in the rim. In the past, 9 mm cartridges were available, as well as .177, .25, etc. cartridges. BB and CB caps were common, as well as .22 Short and .22 Long.

Today, .22 LR (Long Rifle) easily accounts for over 99% of all rimfire ammunition shot. Recently, a .177 rimfire cartridge was released, but whether it catches on is another matter.

Rimfire rounds are normally a soft lead bullet, and can be supersonic or subsonic. They are often gilded with copper to try to keep lead off the hands of the shooter, since it is a low-level poison. This author knows of no non-lead .22 rimfire rounds.

Cartridges in use

There is great variety in the length and diameter of cartridges for the different kinds and calibres of rifles and pistols. The best cartridge for different purposes is subject to much discussion. However there are standard uses for certain calibres, and these are a reliable guide to recommended uses.

It is important to note that equivalent caliber is by no means equivalent power. Generally speaking, "stopping power" is determined by the weight of the bullet, the terminal ballistics of the bullet -- does it stay straight and in one piece, tumble, or "mushroom" on impact -- and the charge of gunpowder accelerating it. For example, a .22 pistol round is almost exactly the same caliber as a .223 NATO rifle round, but the .223 is vastly more powerful.

The following list samples only a few very well-known cartridges; for a complete list, see List of cartridges (weaponry), pistol and rifle. The list is roughly ordered by cartridge power.

  • .22 Long Rifle or .22LR cartridge is used for target shooting and hunting. Despite the name, it is used in some target pistols.
  • 9 mm can refer to a variety of pistol cartridges, but most commonly it means 9 x 19 mm "Luger" or "Parabellum". It is used in a variety of automatic handguns and submachine guns, though law enforcement and military users are moving away due to its poor penetration against body armor.
  • 7.62 x 39 mm cartridges are used in the Kalashnikov AK-47. This is the most fired cartridge in history. Kalashnikov did not invent the "medium power" automatic rifle cartridge, but it brought the concept into practical mass-production.
  • 5.56 x 45 mm is NATO's standard assault rifle and light machine gun cartridge. It is a military adaptation of the Remington .223.
  • 7.62 x 51 mm is NATO's standard sniper rifle and medium machine gun cartridge. In the 1950's it was the standard NATO cartridge for rifles, but recoil and weight proved problematic for the new assault rifles designs such as the FN FAL. It is itself derived from:
  • .30-06, (approx 7.7 mm) the standard US Army rifle cartridge for the first half of the 20th century. It is a "full-power" rifle cartridge suitable for hunting medium sized game. It was most famously used in the M1 Garand semi-automatic rifle.
  • .50 Browning Machine Gun is used in heavy machine guns and super-high-powered sniper rifles by NATO armies. Such rifles are intended for destroying military matériel such as sensitive parts of helicopters and aircraft. Civilian enthusiasts use them for long-distance target-shooting.
See also: List of cartridges (weaponry), pistol and rifle

History

The original cartridge for military small arms dates from 1586. It consisted of a charge of powder and a bullet in a paper tube. Thick paper is still known as cartridge paper from its use in these cartridges.

This cartridge was used with the muzzle-loading military firearm, the base of the cartridge being ripped or bitten off by the soldier, the powder poured into the barrel, and the bullet then rammed home. Before the invention of the firelock or flint-lock, about 1635, the priming was originally put into the pan of the wheel-lock and snaphance muskets from a flask containing a fine-grained powder called serpentine powder. Later the pan was filled from the cartridge above described before loading. The mechanism of the flint-lock musket, in which the pan was covered by the furrowed steel struck by the flint, rendered this method of priming unnecessary, as, in loading, a portion of the charge of powder passed from the barrel through the vent into the pan, where it was held by the cover and hammer.

The next important advance in the method of ignition was the introduction of the copper percussion cap. This was only generally applied to the British military musket (the Brown Bess) in 1842, a quarter of a century after the invention of percussion powder and after an elaborate government test at Woolwich in 1834. The invention which made the percussion cap possible was patented by the Rev. A. J. Forsyth in 1807, and consisted of priming with a fulminating powder made of chlorate of potash, sulphur and charcoal, which exploded by concussion. This invention was gradually developed, and used, first in a steel cap, and then in a copper cap, by various gunmakers and private individuals before coming into general military use nearly thirty years later. The alteration of the military flint-lock to the percussion musket was easily accomplished by replacing the powder pan by a perforated nipple, and by replacing the cock or hammer which held the flint by a smaller hammer with a hollow to fit on the nipple when released by the trigger. On the nipple was placed the copper cap containing the detonating composition, now made of three parts of chlorate of potash, two of fulminate of mercury and one of powdered glass. The detonating cap thus invented and adopted, brought about the invention of the modern cartridge case, and rendered possible the general adoption of the breech-loading principle for all varieties of rifles, shot guns and pistols.

Probably no invention connected with firearms has wrought such changes in the principle of gun construction as those effected by the "expansive cartridge case." This invention has completely revolutionized the art of gunmaking, has been successfully applied to all descriptions of firearms, and has produced a new and important industry -- that of cartridge manufacture.

Its essential feature is the prevention of all escape of gas at the breech when the weapon is fired, by means of an expansive cartridge case containing its own means of ignition. Previous to this invention shot guns and sporting rifles were loaded by means of powder flasks and shot flasks, bullets, wads and copper caps, all carried separately. The earliest efficient modern cartridge case was the pin-fire, patented, according to some authorities, by Houiller, a Paris gunsmith, in 1847; and, according to others, by Lefaucheux, also a Paris gunsmith, in or about 1850. It consisted of thin weak shell made of brass and paper which expanded by the force of the explosion, fitted perfectly into the barrel, and thus formed an efficient gas check. A small percussion cap was placed in the middle of the base of the cartridge, and was exploded by means of a brass pin projecting from the side and struck by the hammer. This pin also afforded the means of extracting the cartridge case. This cartridge was introduced in England by Lang, of Cockspur Street, London, about 1855.

The central-fire cartridge was introduced into England in 1861 by Daw. It is said to have been the invention of Pottet of Paris, improved upon by Schneider, and gave rise to much litigation in respect of its patent rights. Daw was subsequently defeated in his control of the patents by Eley Bros. In this cartridge the cap in the centre of the cartridge base is detonated by a striker passing through the standing breech to the inner face, the cartridge case being withdrawn, or, in the most modern weapons, ejected by a sliding extractor fitted to the breech end of the barrel, which catches the rim of the base of the cartridge.

This is practically the modern cartridge case now in universal use. In the case of shot guns it has been gradually improved in small details. The cases are made either of paper of various qualities with brass bases, or entirely of thin brass. The wadding between powder and shot has been thickened and improved in quality; and the end of the cartridge case is now made to fit more perfectly into the breech chamber. These cartridges vary in size from 32 bore up to 4 bore for shoulder guns. They are also made as small as .410 and .360 gauge: their length varies from 1¾ to 4 inches (44 to 102 mm). Cartridges for punt guns are usually 1½ inches (37 mm) in diameter and 9¾ inches (248 mm) in length.

In the case of military rifles the breech-loading cartridge case was first adopted in principle by the Prussians about 1841 in the needle-gun breech-loader. In this a conical bullet rested on a thick wad, behind which was the powder, the whole being enclosed in strong lubricated paper. The detonator was in the hinder surface of the wad, and fired by a needle driven forward from the breech, through the base of the cartridge and through the powder, by the action of a spiral spring set free by the pulling of the trigger.

In 1867 the British war office adopted the Eley-Boxer metallic central-fire cartridge case in the Enfield rifles, which were converted to breech-loaders on the Snider principle. This consisted of a block opening on a hinge, thus forming a false breech against which the cartridge rested. The detonating cap was in the base of the cartridge, and was exploded by a striker passing through the breech block. Other European powers adopted breech-loading military rifles from 1866 to 1868, with paper instead of metallic cartridge cases. The original Eley-Boxer cartridge case was made of thin coiled brass. Later the solid-drawn, central-fire cartridge case, made of one entire solid piece of tough hard metal, an alloy of copper, &c., with a solid head of thicker metal, has been generally substituted.

Central-fire cartridges with solid-drawn metallic cases containing their own means of ignition are almost universally used in all modern varieties of military and sporting rifles and pistols.

Around 1970, machined tolerances had improved to the point that the cartridge case was no longer necessary to seal a firing chamber. Precision-faced bolts would seal as well, and could be economically manufactured.

Problems

The conventional cartridge also adds certain problems to the gun.

Also, it had become well-known that the cartridge is both expensive and heavy, and the single most difficult part to manufacture. Generally, they were manufactured by deforming a disk of brass with a series of progressive dies. Cases are generally round, and this decreases the volumetric efficiency of the gun's magazine. A caseless cartridge can have the propellant molded in a square shape.

The gun has to have an ejection port to eliminate the spent cartridge-case. This means that dirt and fluid can enter the gun through the ejection port.

The primer, and associated firing pin add a delay between the time the trigger is pressed and the time the bullet leaves the barrel. Experiments had decisively demonstrated that this delay reduced accuracy for most shooters. A popular accessory, available for many guns, were "low mass" firing pins and hammers, often made of titanium, that would reduce the time to fire the percussion cap.

On the flip side, the case helps carry heat away from the firing chamber.

Reloading

Some shooting enthusiasts reload their spent brass cartridges. By using a press and a set of dies, one can reshape, deprime, reprime, recharge the case with gunpowder, and seat and crimp a new bullet. One can do this at about half the cost of purchasing factory ammo. It also allows one to use different weights and styles of bullets, as well as varying the powder charge which affects accuracy and power. Enthusiasts usually only reload boxer primed cartridges as the process is more easily automated than berdan priming.

See: Handloading.

Caseless ammunition

Main article: Caseless ammunition

Around 1989, Heckler und Koch, a prominent German firearms manufacturer, began making press releases about the G11 assault rifle, which shot a 4.75x33 square caseless round. The round was mechanically fired, with an integral primer.

In 1993 Voere of Austria began selling a gun and caseless ammunition. Their system used a primer, electronically-fired at 17.5 ± 2 volts. The upper and lower limits prevent fire from either stray currents or static electricity. The direct electrical firing eliminates the mechanical delays associated with a striker, making any shooter more accurate.

In both cases, the "case" was molded directly from solid nitrocellulose, which is itself relatively strong and inert. The bullet and primer were glued into the propellant block.

See also

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External links

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