May 16, 2004


The first and simplest way to harm an enemy at distance is to throw an object at him/it.
Probably the first projectiles were naturally occurring stones, but soon humans figured out several ways to impart more speed to projectiles, because more speed means more lethality and increased range. These first weapons were slings, bows and sort of levers used to impert more speed to spears. Also the projectiles evolved, becoming accurately shpaed stones or pellets, arrows, spears, and later incendiary mixtures, like tar and saltpeter.
For many centuries, the situation remained the same: same kind of projectiles, same kind of machines to launch them (only the Chinese developed long ago propellants and rockets to be used as weapons and signals). Only the size increased: the Middle Age siege catapults were monster capable of throwing stones of some hundred kilos at a distance of several hundred of meters; crossbow flechettes could pierce the heaviest body armor at considerable distance.

The most basic equation to know about projectiles and bullets is this: the kinetic energy of a moving body is proportional to its mass and to the square of its speed. In short:

Ek = 1/2 * m * v^2

If we express mass in kg and speed in m/s, the resulting energy is in Joules.
It's clear that increasing speed is the best way to increase energy; but there is a limit to the speed obtainable with mechanical propulsion methods.

When finally firearms were invented, things come to an abrupt change: even clumsy as they were at the time, firearms rapidly surpassed any other weapon in terms of range and lethality. The performance of today's firearms are stunning: sniper rifles have an effective range of almost 1000 m - if fired by a properly trained shooter, of course. Machine guns have fire rate of hundred of shots per minute and effective range of 3000 m.
A firearm is a device used to transform the chemical energy of the propellant (a substance or mixture capable of very fast combustion) in kinetic energy of the projectile - called bullet in case of small arms, but also slug or ball, depending from the kind of firearm and characteristics of the projectile. Shell usually indicates a large caliber projectile (from 20-25 mm upwards) loaded with explosive, incendiary mixtures or other substances.
The great quantity of hot gases produced by the burning propellant expand in the gun's barrel and thus exert a force on the bullet, accelerating it through the barrel. The initial speed varies from 250-300 m/s for handguns and shotguns, to 900 m/s for precision rifles. Cannons (from 20mm upwards) can have even higher muzzle speed. Nowadays, usually bullet, propellant and primer are combined in a single piece called cartridge: cartridge cases can be made of plastic (for shotguns and military combustible cases), carboard (hunting rifles), or brass - the most common option.
Shotguns have a smooth barrel (or barrels), and they usually fire a cartridge containing a number of small, spherical, lead bullets: these weapons are mostly used to hunt birds and other small animals at relatively close range (50 m); shotguns loaded with heavy shots are very effective against personnel in close combat situations.
Other guns have rifled barrels, which have twiststing grooves on the inner surface: the scope of these grooves is to impart to the bullet a rotation around its longitudinal axis, in order to have a more stable trajectory.

Bullets are usually made of lead, because it's a dense metal, cheap and easy to cast and machine; high-performance ammunitions need a brass-jacketed bullet (Remember Full Metal Jacket, the movie?) because lead is too soft and it would be sheared off by the rifling grooves while accelerating through the barrell.

Bullets come in many different styles, but basically they are optimized either for penetration or stopping/killing power. To achieve the maximum effectiveness, in fact, a bullet should transfer all of its kinetic energy to the target, but a very strong bullet, optimized for penetration, is very likely to pierce the target from side to side (the "target" in this discussion is usually assumed to be a human body) and reatin some energy. In military apllications, this usually is not a big problem: a wounded man is more a burden for an army than a dead man (a wounded needs to be evacuated and treated); international treaties impose some regulations on the bullets to use etc. Jacketed bullets also offer a good penetration against body armor and thin metal barriers (think of a car's door, that unlike we see in movies, gives only a minimal protection), and special bullets with a dense core (usually tungsten carbide) can be effective even against ligthly armored vehicles.

In the field of law enforcement, personal defense and hunting (the worst possible outcome for a hunter is to have a wounded prey fleeing and getting lost), on the other hand, it is required to kill or incapacitate the target in the most effective way, possibly with a single shot. But range and accuracy are still important. For this reason, a variety of deformable balls has been developed. These bullets are explicitly designed to expand upon impact, in order to cause deep and extended wounds, transfer more energy and produce a shockwave in the target's tissue: the shockwave alone is enough to damage vital organs.

What's in the future for bullets? Electromagnetic guns have the potential to fire bullets at speeds of kilometes per second, but they're still in development phase. They might be fielded in a ten years, I suppose.
For the moment, respect firearms, and learn about them, because a gun is no joke: it's built to kill.


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