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What is a gun?Edit
A gun, or more properly a firearm, is a tool designed to accelerate an object (the projectile) to a relatively high velocity, and propel it with a significant degree of accuracy to impact a distant target. The target can be anything, paper, clay, steel, or a living being, etc. The expected distance to the target, the type of target, and the desired effect on the target will all shape the best type of firearm and ammunition to use, as will other concerns such as size, weight, and cost, and the shooter's abilities.
- Bullet, slug, pellet--The projectile launched from a firearm, generally consisting primarily of lead or some other dense metal. Bullets are fired from rifles and handguns, while slugs and pellets are fired from shotguns.
- Cartridge--A self contained unit containing primer, gunpowder, and bullet, generally held in a metallic (generally brass or steel, though other metals have been used) case.
- Ammunition--Collective term for multiple cartridges.
- Action--The means by which a gun is loaded and fired. Examples are: lever action, bolt action, Slide action (also called "pump" action), semi-automatic, break-open, etc.
- Magazine--A spring-loaded container for feeding cartridges into a firearm's chamber. May be integral or detachable.
- Clip--A device for holding cartridges into a magazine; also commonly (though incorrectly) used as a synonym for magazine
- Chamber--Where the cartridge is held when it is fired; generally part of the barrel assembly, except in the case of revolvers.
- Caliber--Size (diameter) of the bullet in inches. Examples: .357 Magnum, .45 Auto. May also be used colloquially to describe size of the bullet, without regard to unit of measurement.
- Magnum--The term "Magnum" is commonly applied to a very powerful cartridge that was either developed from an earlier, less-powerful cartridge, or is more powerful than most cartridges that use the same size bullet. Examples: The .357 Magnum was developed from the .38 Special. Both use .357-inch bullets. The 7mm Magnum was not developed from the 7mm Mauser, but is far more powerful.
- Millimeter--One thousandth of a meter (approximately .0394 inch); bullets are commonly measured using this system of measurement, and width and length are denoted, in that order. Example: 9x19mm, 5.56x45mm, 7.62x51mm. Sometimes, only the width (diameter) is mentioned. Example: 9mm, 10mm, 7.62mm, 5.56mm
Types of gunsEdit
Guns are generally divided into 3 broad classes; rifles, shotguns, and handguns. Often rifles and shotguns are lumped together as long guns. Handguns are often more tightly restricted than long guns, due to their smaller size and easy concealability. There are also machine guns and submachine guns, which are often preferred by militaries & law enforcement agencies.
A rifle takes its name from the rifling, or spiral grooves cut on the inside of the barrel. These grooves spin the bullet, and provide stability to keep it from tumbling as it flies through the air. Firearms without rifling generally fire spherical projectiles, which tumble in random directions (like a knuckleball) as they fly, and thus are fairly inaccurate. By adding rifling, not only is the random tumbling replaced with a consistent behavior in flight, but the bullet's shape can vary widely. In particular, rifling allows a long, slender bullet to be used to reduce air resistance, and the presence of a distinct front and rear allows the bullet to be constructed for maximum aerodynamic efficiency, or to allow specific structural features.
In addition to the rifled barrel, the word "rifle" also implies a relatively long barrel and a shoulder stock, allowing the rifle to be supported at 3 points; both hands and one shoulder. This 3 point support allows the shooter excellent control over the rifle, and makes rifles relatively easy to shoot accurately. Most rifles have barrels of about 16 to 26 inches in length. A rifle with a barrel length of about 16 inches or less is often called a carbine. Under US law, the minimum barrel length for a rifle is 16 inches; shorter than that and it is classified as a short-barreled rifle and subject to restrictions similar to those that apply to machine guns; a $200 tax stamp is required to put the weapon on the NFA registry.
Rifle bullets are capable of very high velocities, up to 4350 feet per second in the case of the .223 WSSM, the current fastest commercial cartridge. Readily available bullet diameters range from .17 inch to .50 inch; while larger calibers do exist, they are considered under US law to be destructive devices and are subject to restrictions.
A shotgun takes its name from the fact that it is designed to fire shot, a large number of pellets that are smaller than the bore diameter. Shotguns do not generally have rifling, unless they are special slug guns designed to fire special shotgun slugs, which are basically large bullets. Firing shotshells through a rifled barrel will spin the shot and make it spread faster than normal, which is undesirable in most cases.
A smoothbore shotgun barrel generally isn't a straight cylinder, but contains a constriction at the muzzle end, called a choke, that affects how much the shot spreads upon exit from the barrel. A barrel with no choke is called a cylinder bore, and provides the greatest spread, while a full choke provides a large degree of constriction and much smaller diameter patterns. Shotguns designed to shoot at small, fast moving targets should use the most open choke that provides a sufficient density of pellets to guarantee a hit at the appropriate range. Short ranges, then, call for open chokes, while long ranges call for tighter chokes. Most modern shotguns are available with screw-in chokes, which allow the shooter to change the constriction by simply unscrewing one choke and screwing in a new one. A double-barreled shotgun usually provides the shooter with the capability of having two different chokes, one for short range and one for long range.
Shot pellets used in shotshells are broken into two basic classes, buckshot and birdshot. Buckshot are large balls that are stacked into the case one by one, while birdshot is much smaller and poured into the case by weight. Birdshot is used, as the name implies, for birds, as well as clay targets. Buckshot, again as the name implies, is used for hunting larger game such as deer, as well as for military and defensive use. Shot is characterized by a size number. The larger the number, the smaller the shot size. #12 shot is commonly found in .22 caliber cartridges, and is called rat-shot. #9 is generally the smallest used for hunting game birds or shooting clay targets. Larger sizes are used for larger game and longer ranges, and the largest sizes, like BB, T, TT, and TTT are found in steel shot used for hunting waterfowl (lead shot is banned for waterfowl due to the likelihood of ingestion by birds). Buckshot starts at #4 buck, and goes past #1 to 0000 (called "quad-ought", 000 (triple-ought), 00 (double-ought), and 0 (ought). Size 00 is the most commonly used type by military and police, and is .33 inches in diameter.
There are two types of slugs available for shotguns, rifled slugs and saboted slugs. Rifled slugs are near bore size, have spiral grooves resembling rifling cast into the outside of the slug, and are designed with a deep hollow in the rear. The combination of weight-forward design and slow spin introduced by air traveling past the grooves provide stability from a smooth barrel. Saboted slugs use smaller diameter projectiles in an axially split plastic cup, the sabot, that drops off after the slug exits the barrel. Saboted slugs generally must be fired from a rifled barrel, as they have no other means of providing stability. Saboted slugs have better accuracy and retained velocity than rifled slugs and thereby a substantially greater effective range, as much as 100 yards or more.
Handguns, like rifles, have a rifled barrel and are designed to fire a single bullet at a time, By virtue of their size and shape, they can be held and fired with one hand, although a two-handed hold is usually possible, thereby providing greater stability and accuracy when using the proper shooting technique. Handguns are more difficult than long guns to shoot accurately, due to the absence of a supporting stock, and the resulting lack of control. Handguns are generally designed to be much lighter and more portable than rifles, though some types used for long range target shooting or hunting may have barrels up to 14 inches or more. A handgun designed for self-defense use and easy carry will generally have a barrel under 6 inches in length, and weigh 2 to 3 pounds or less. Because of the short barrel and the inability of pistol designs to tolerate very high pressures, pistols generate far less bullet velocity than rifles. There is also the issue of recoil; cartridges loaded to higher pressures will generate more recoil. If the weapon has less mass, or poorly distributed mass, more recoil will be felt, making follow-up shots slower.Handguns are divided into two main categories, revolvers and pistols. A revolver is a handgun with multiple chambers and one barrel, while a pistol has a barrel assembly, in which the chamber and barrel are integral. The term "pistol" is often used as a synonym for handgun, including revolvers, though the term "revolver" is never used to refer to a pistol (except in British movies).
Handguns are generally used for two purposes; self-defense, or to provide more challenge to a recreational shooter. The easy portability of the handgun is what makes it a common choice for defense—and for criminal activity. Because of this, handguns are much more severely restricted by governmental agencies than are long guns.
To provide adequate stopping power for defensive hand guns, normal bore sizes range from .30 to .45 caliber, although specialized target and hunting weapons are available from .17 to .50 caliber. Velocity levels generally run from 800 to 1500 feet per second.
Ballistics is the study of how projectiles behave in flight, and when applied to firearms, ballistics is divided up into three areas, internal, external, and terminal ballistics. Internal ballistics is what happens from the point the cartridge is ignited until the point it leaves the barrel, external ballistics covers from there to the point where the bullet hits the target, and terminal ballistics covers from that point until the bullet stops. A basic understanding of ballistics will help in choosing a firearm and ammunition for a given task.
The driving force behind internal ballistics is gunpowder. Modern "smokeless" gunpowder is a mixture of nitrocellulose and nitroglycerin, along with various additives to control burn rate, muzzle flash, and other properties. Fast burning powders, like those used in non-magnum handgun cartridges and shotguns shells, have up to 50% nitroglycerin, generate pressure quickly from small amounts of powder. Slower powders, such as those used in magnum rifle cartridges, have little or no nitroglycerin, and burn slower and require more powder to generate the high pressures needed. One of the vital characteristics of smokeless powder is that the rate at which it burns increases with the pressure; since burning faster generates higher pressures, this creates a feedback cycle. Take a small quantity of rifle powder, for example, and lay it out in a line on the ground and ignite it, and it may take a couple of seconds to burn, yet when ignited in the confined space of a rifle chamber, it will burn in milliseconds. Black powder, which was used up into the late 1800s, doesn't have a pressure dependent burn rate, and will instantly ignite even when unconfined. The pressure dependent characteristic of smokeless powder not only makes it safer than black powder, since it doesn't have explosive effects unless confined, but it also makes it capable of safely generating far higher bullet velocities than are possible with black powder. Black powder cartridges operate at pressures of up to 20,000 psi, while modern cartridges operate at pressures of up to 60,000 psi.
If you were to chart the pressure in a firearm's barrel during firing, what you'd see is a very steep rise in pressure at the beginning, as the primer ignites the powder and the pressure starts to rise, and the burn rate goes up in a feedback loop. The pressure will quickly reach the point where it can force the bullet out of the case and into the barrel. While the force with which the bullet is held in the case has some effect, the major limiting factor will be the inertia of the bullet. Once the bullet begins to accelerate, the volume behind the bullet will begin to increase rapidly. Very shortly the bullet will be moving faster than the powder can burn, causing the pressure to drop (this is why the breech end of the barrel is generally much thicker than the muzzle end). When the bullet reaches the end of the barrel, any remaining pressure is released, causing the muzzle blast.
If you were to chart the pressure curve, and measure the area under the curve, that area would be equal to the energy of the bullet when it leaves the barrel. To get more energy, then, you need more area under the curve. There are two ways to do that; one is to raise the height of the curve overall, and the other is to widen the curve, so the pressure drops off more slowly. A higher curve means more peak pressure, and that means a stronger gun is needed to contain the pressure. A wider curve means a slower, less efficient powder (and thus a larger case) and a significant increase in the muzzle blast.
A heavy bullet will accelerate slower, and will produce higher pressures for a given load of powder than a light bullet will. Because of this, slower powders are used with heavier bullets; the greater resistance provided by the bullet will keep the pressure in the chamber higher for a longer period of time, allowing the same peak pressure to be reached. Often the same bullet energy can be produced by a smaller quantity of powder if a heavy bullet and slow powder are used, compared to a light bullet and a fast powder. Generally this doesn't affect someone buying factory loaded cartridges, but when handloading, careful consideration of bullet weight and powder burn rate can have a significant impact on the cost of loading a round of ammunition.
External ballistics are primarily governed by two things: the bullet's shape and its sectional density. The impact shape should be fairly obvious; streamlined shapes slip through the air with less resistance than non-streamlined shapes, so a pointed bullet will have less drag than a flat nosed bullet of the same size. The sectional density can have significantly more effect, since that's the "engine" that moves the bullet through the air. Sectional density is calculated by dividing mass of the bullet the frontal surface area. Given two bullets of the same diameter, one twice as heavy as the other, the heavier bullet will have twice the sectional density, and thus will have twice the inertia to push aside the same amount of air. Since frontal surface area increases as the square of the caliber, and bullet mass for similarly shaped bullet increases as the cube of the caliber, doubling the caliber will roughly double the sectional density. This means an aerodynamic .22 caliber bullet may not travel as well as a blunt .44 caliber bullet, because the bullet shape will have to cut the drag in half to compensate for the lower sectional density. Target shooting at 1000 yards requires special, extra long, ultra-low drag bullets in .22 caliber, but a blunt, nearly cylindrical hunk of lead will work fine in .45 caliber.
The other issue with external ballistics is the bullet drop. As soon as the bullet leaves the barrel, gravity starts to accelerate it downwards at a rate of 32 feet per second, every second. This quickly adds up, requiring the shooter to aim well above the target so the bullet will fall down to the level of the target by the time it hits. While most long range sights will have a way to compensate for this, by adjusting the sight based on the range to the target, at long enough ranges the drop is such that an error of a few percent in the range to the target can result in a miss. Since all bullets accelerate downwards at the same rate, regardless of how fast they are moving, a faster bullet will reach the target before it can drop as far as a slow bullet traveling the same distance.
The desired terminal effect of a bullet can range from just the need to punch a hole in a piece of a paper, to the need to stop a charging Cape Buffalo before it can trample the shooter into the dirt. The first requires very little energy—just enough to carry the bullet to the target is more than enough—while the second requires the energy to penetrate skin, muscle, and perhaps even bone to reach the target's vital organs or central nervous system and ensure a quick stop.
In general terms, the penetration ability of a bullet is determined by its momentum, which is defined as the mass of the bullet, multiplied by its velocity. This momentum works against the momentum of the target; since momentum is conserved in any collision, a bullet can only push a certain amount of material out of its way before its momentum is drained, and it comes to a stop. The amount of material the bullet must push out of the way is determined by the bullet's shape and diameter. The diameter is easy to deal with; a bullet with one inch of frontal area must push a one inch area hole through the target to penetrate it. The shape of the bullet determines how quickly the bullet must push aside the target material; a long, gradual taper will push the target material to the sides gradually, while a flat faced bullet will have to push it out of the way all at once. This is the same reason a long, pointed nose on a rocket allows it to slip easily through the air, while a flat nose produces more drag. A pointed, aerodynamic bullet will, other factors constant, penetrate further than a blunt, round nosed bullet, which will penetrate farther than a flat nosed cylinder.
Another issue with penetration is stability. The long, pointed nose of most rifle bullets results in the center of gravity being in the rear half of the bullet, often far to the rear. This means that the bullet would rather fly back first, and only the rifling prevents this from happening in the air. When a target is hit, the resistance is so much greater that no practical amount of rifling twist could keep the bullet pointed forwards, so the bullet will tumble. The bullet will generally flip 180 degrees, and if it does not break apart, will continue to travel through the target base first, which limits penetration.
Bullets used for hunting and defense need to be able to penetrate to at least a minimum depth to reach the vital organs and/or the central nervous system, to ensure a quick incapacitation of the target. Ideally a vital organ, such as the heart or spine, will be hit, causing a nearly instant incapacitation; if this is not the case, then the bleeding of the wound channel will, if sufficiently large, eventually cause sufficient blood loss to incapacitate the target. Incapacitation by blood loss is not ideal, however, since it takes time that the target could use to attack you (in a defensive situation) or run away (in a hunting situation), requiring a lengthy tracking.
A larger bullet diameter will both increase the chances of hitting a vital organ by producing a wider path through the target, and also increase the rate of blood loss. This is the reason that most hunting and defense ammunition uses expanding bullets; these bullets expand to a larger diameter upon impact, producing a larger wound channel. Since the goal is still to hit a vital organ, the penetration must still meet the minimum requirements, but any momentum the bullet possesses beyond what is required to reach that depth can be used to expand the bullet and create a larger wound channel.
A completely different method of wounding is used by the smoothbore shotgun. By firing multiple pellets, each with sufficient momentum to penetrate to the desired depth, multiple wound channels are created. This vastly increases the chances of hitting a vital organ, and also produces multiple wound channels to speed blood loss. It is this factor that makes the police or military riot shotgun such a formidable weapon, at least at short ranges where multiple pellet hits on the target can be expected.
Firearm accuracy is a combination of many factors, spread across three factors: gun, ammunition, and shooter. For top accuracy, all three factors, and their interactions, must be addressed. The primary element in all three is consistency. If everything happens as close to possible the same way every time, then the bullet should strike as close to possible to the same spot every time.
The first factor is the inherent precision of the firearm itself. The barrel must grip the bullet tightly and consistently, apply the right amount of spin, and release the bullet with minimal disturbance. The sights must consistently align with the barrel from shot to shot. The cartridge must be firmly held in the chamber, so that it cannot shift under the force firing, as this might disturb the bullet as it exits the case or change the pressure in the barrel and thus change the bullet's velocity. The gun must behave consistently under recoil; a loose and shifting barrel, for example, would allow the barrel to shift before the bullet exits, and send it in a slightly different direction each time. Even the vibrations of the barrel can alter the path of the bullet; a long, thin barrel will vibrate more than a short, fat barrel and this will be more prone to spread shots around.
The next factor is the ammunition. The bullet must closely match the bore diameter, so that a good seal is formed; too small and gas will blow by, too large and excessive pressure and bullet deformation will occur. The correct amount of powder must be present, and it must burn at the same rate, so it pushes the bullet down the barrel to the same velocity each shot. The bullet must also sit in the case right; too deep and pressures will go up, too loose and the pressures will go down. The bullet itself must be a consistent weight, and well balanced, with no voids and no damage.
The last factor is the shooter. The shooter needs to have a consistent stance, grip, and pull of the trigger, so that every time the trigger is pulled everything happens in the same way. Much of this is skill, but a good deal of it is also ergonomics of the gun. A light, consistent trigger pull, a comfortable, well fit stock or grips, and good sights all help a shooter control the firing process. A gun that is to be fired without a rest should be light enough to not cause fatigue, but also heavy enough to hold steadily and tame the recoil of the cartridge. An optic helps most shooters, as it is easier to focus on the target and reticle when they fall in the same focal plane, and magnification will help shooters with poor eyesight place their shot more accurately. Too much magnification, however, results in a tiny field of view, and high magnification also magnifies the shooter's tremble, which can be distracting.
Accuracy is generally measured in one of two ways; either by the center-to-center measurement of the furthest two shots in a group of shots fired at a given range, or in minutes of arc (MOA). Since one MOA equals about 1.047 inches at 100 yards, it's fairly easy to convert from group size to MOA, though it can be misleading, since a gun that shoots 1 MOA at 50 yards probably won't shoot 1 MOA at 100 yards. Still, MOA is commonly encountered, and a rifle that will shoot 1 MOA at 100 yards is considered to be highly precise. Some long range hunting and target handguns, like the Remington XP-100 or the Thompson Center Contender, are capable of 1 MOA accuracy, but for the average defensive handgun, a group of several inches (around 5) at 25 yards is more than acceptable precision. The most accurate defensive type pistols, generally found in Bullseye pistol shooting, can group shots in under 2 inches at 50 yards.