Cartridge (firearms)
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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. A cartridge without a bullet is called a blank.
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[edit] Design
The cartridge case 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, allowing the cartridge case to be removed from the chamber.
Critical specifications include 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 typically the diameter of the barrel's lands (or sometimes the diameter of the bullet itself), and the second is the length of the cartridge case. For example, the 7.62 x 51 mm uses a bore diameter of 7.62 mm and has an overall case length of 51 mm.
One should be aware that cartridge nomenclature is inconsistent and unhelpful when trying to determine dimensions, tolerances or indeed almost any other characteristic of a given round. The .38 Special actually has a bullet diameter of 0.357" (jacketed) or 0.358" (lead) while the case has a diameter of 0.380". The .357 Magnum is a direct evolution of the .38 special, but differently named, and no reference is made to the longer case. The .30-06 rifle round is a (nominally) .30" caliber round designed in 1906; and the .303 British round may vary wildly in actual dimensions (as do the surviving rifle chambers of its era).
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 pistolfire is not solely determined by the ammunition; the accuracy and doctrine of the shooter contribute a great deal as well.
Of the hundreds of different designs and developments that have occurred, essentially only two basic cartridge designs 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.
[edit] Centerfire
Centerfire cartridge designs use a centrally located primer, which, in most cartridges used by civilians, can be replaced, so that the expensive brass cartridge cases can be reused. These cartridges are 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 simpler for irregular 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.
[edit] Rimfire
Rimfire cartridges, of which only the popular .22 LR remains in common use, were a popular solution before the centerfire design was fully perfected. They 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 .17 HMR (.177 caliber) rimfire cartridge was released, and has become extremely popular among target shooters as well as small game hunters, due to its high velocity and flat shooting characteristics. Rimfire rounds normally use a soft lead bullet, and can be supersonic or subsonic. They are often gilded with copper both for toxicity reasons and to prevent barrel fouling. However, some of the newer .177 rounds feature ballistic plastic tips and are solid copper.
[edit] 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 Remington (5.56 x 45 mm 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 usually used for target shooting and hunting, although because of its small size, it can be used in small, light, and easily concealable self-defense handguns as well. (Despite its name, it is often fired in pistols and revolvers in addition to rifles.) It is the most commonly fired cartridge ever in the history of firearms, mainly because rimfire ammunition is much cheaper to produce than centerfire and because the recoil from the small .22" projectile being accelerated to relatively low velocities is very mild.
- 9 mm can refer to a variety of pistol cartridges, but most commonly it means the 9 x 19 mm "Luger" or "Parabellum" round. It is used in a variety of automatic handguns and submachine guns, though law enforcement and military users are moving away from this cartridge due to the lower number of instances of one-shot stops (a stop being incapacitation of the target either due to death or grievous injury) when compared to such rounds as the .40 S&W and the classic .45 ACP.
- 7.62 x 39 mm cartridges are used in the Kalashnikov AK-47. This is the most fired centerfire 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 .223 Remington.
- 7.62 x 51 mm is NATO's standard sniper rifle and medium machine gun cartridge. In the 1950s 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, (7.62 x 63 mm) was 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.
- .338 Lapua (8.6 x 70 mm or 8.58 x 71 mm) is a specialized rimless centerfire cartridge developed for sniper rifles. The .338 Lapua is a dual purpose anti-personnel and anti-materiel round for long-range shooting. In addition, with its increased popularity it is being used by Big-game hunters.
- .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.
[edit] 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 flintlock, about 1635, the priming was originally put into the pan of the wheellock and snaphance muskets from a flask containing a fine-grained powder called serpentine powder.
The evolving nature of warfare required a firearm which could be fired more rapidly, resulting in the flintlock musket (and later the Baker rifle), in which the pan was covered by furrowed steel. This was struck by the flint and fired the weapon. In the course of loading a pinch of powder from the cartridge would be placed into the pan as priming, before the rest of the cartridge was rammed down the barrel, providing charge and wadding.
Later developments (c1835?) 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, shotguns 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 shotguns 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,[attribution needed] by Houiller, a Paris gunsmith, in 1847; and, according to others,[attribution needed] by Lefaucheux, also a Paris gunsmith, in or about 1850. It consisted of a 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.
As a result of the relatively low pressures involved, cartridges used in modern shotguns have changed very little since the invention of the center-fire primer. The only changes are that the cases may be made of paper, plastic, and/or metal; the wadding between powder and shot is now made of modern materials; and the end of the cartridge case is more precisely fitted to the breech chamber, which ranges in modern shotguns from .410 gauge (.410 inches) to 10 gauge (.770 inches) (gauge is measured by the number of equal-sized balls that can be formed of a pound of pure lead; a 12-gauge shotgun has a bore of .770 inches, which is the diameter of a 1/12 pound ball of lead).
Rifle cartridges, on the other hand, have undergone significant changes as the pressures involved have increased. 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 the American Civil War (1861-65) a breechloading rifle, the Sharps, was introduced and produced in large numbers. It could be loaded with either a ball or a paper cartridge. After that war many were converted to the use of metal cartridges. The invention by Samuel Colt of revolver handguns that used metal cartridges established cartridge firearms as the standard thereafter.
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 - occasionally these cartridges could break apart and jam the breech with the unwound remains of the casing upon firing. Later the solid-drawn, central-fire cartridge case, made of one entire solid piece of tough hard metal, an alloy of copper, 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.
[edit] Problems
The conventional cartridge also adds certain problems to the gun.
The casing 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. Dirt and fluid can enter the gun through the ejection port and adversely affect functioning. Stoppages can occur if a badly cleaned or maintained weapon fails to properly eject a spent casing, which will subsequently block the passage of the next live round from the magazine to the chamber.
The primer, and associated firing pin add a short 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. Light replacement firing pins and hammers have been produced to minimize the delay.
[edit] 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 ammunition. It also allows one to use different weights and shapes 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.
[edit] Caseless ammunition
Around 1989, Heckler & 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, reducing reaction time (lock time), and allowing for easier adjustment of the rifle trigger.
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.
[edit] Blank ammunition
A blank is a charged cartridge that does not contain a projectile - the opening where the projectile would be held is crimped shut or sealed with some material that will disperse rapidly upon leaving the barrel, in order to contain the propellant. It should be noted when firing blank ammunition that this sealing material can still potentially cause harm at extremely close range. Blanks are used in training, but do not always cause a weapon to behave in an identical way to when using live ammunition - recoil will almost always be far weaker, and some automatic weapons will only cycle correctly when the weapon is fitted with a blank-firing adaptor to confine gas pressure within the barrel in order to operate the gas system. Blanks may also be used to launch a rifle grenade, although later systems used a grenade designed to capture a bullet from a conventional round, speeding deployment and negating the risk of mistakenly firing a ball round up the back-side of a rifle grenade on the end of one's own gun. Blanks may also be used in dedicated launchers for propelling a grapnel, rope line or flare, or for a training lure for training gun dogs. The propellant cartridges used in a heavier variety of nail gun are essentially rimfire blanks.
[edit] Drill rounds
Drill rounds are inert versions of cartridges used for education and practice during military training. Other than the lack of propellant, they are the same size as normal cartridges and will fit into the mechanism of a weapon in the same way as a live cartridge. To distinguish them from live rounds they are marked distinctively. Several forms of markings may be used; eg setting coloured flutes in the cartridge, drilling holes through the cartridge, colouring the bullet or cartridge, or a combination of these. In the case of centrefire drill rounds the primer will often be absent, its mounting hole in the base left open. Because they are mechanically identical to live rounds, which are intended to be loaded once, fired and then discarded, drill rounds have a tendency to become significantly worn and damaged with repeated passage through magazines and firing mechanisms, and need to be frequently inspected to ensure they are not so degraded as to become unusable - for example the casings can become torn or misshapen and snag on moving parts, or the bullet can become separated and stay in the breech when the cartridge is ejected.
[edit] See also
- Category:Pistol and rifle cartridges
- List of rifle cartridges
- List of handgun cartridges
- Table of pistol and rifle cartridges by year
- Ammunition
- Bullet
- Percussion cap
- Nitrocellulose
- Simunition
- Antique guns
