Monday, May 14, 2012

How guns fire bullets

Bullets and missiles come in all shapes and sizes. At 21.8 meters (71 ft) long, one of theworld's biggest intercontinental ballistic missiles, the US Airforce LGM-118A Peacekeeper, is three times the length of astation wagon (estate car)! But it works pretty much the same way as a handgun bullet the size of your pinkie.

What's inside a bullet?
... Bullets are a bit like fireworks and they are arranged in three sections: the primer, the propellant, and the bullet proper. At the back, the primer (or percussion cap ) is like the fuse of a firework : a small fire that starts a bigger one. The next section of the bullet, effectively its "main engine," is a chemical explosive called a propellant . Its job is to power the bullet through the air from the gun to the target. The front part of the bullet is a tapering metal cylinder that hits the target at high speed. It tapers to a point to help it penetrate through metal, flesh, or whatever else the target may be made from.
Artwork: The three main parts of a bullet. 1) The primer "launches" the bullet by igniting the propellant. 2) The propellant accelerates the bullet down the gun. 3) Andthe bullet proper, at the end, is the part that actually does the damage. This one has a complete outer casing known as a full-metal jacket , which means it can be fired faster and further, but it retains its shape on impact. Bullets with a softer pointspread out on impact and do more damage, but don't travel as fast or far.
What happens when you fire?
Bullets are designed to be (relatively) safe until the moment when you fire them. When you pull the trigger of a gun, a spring mechanism hammers a metal firing pin into the back end of the bullet, igniting the small explosive charge in the primer. The primer then ignites the propellant—the main explosive that occupies about two thirds of a typical bullet's volume. As the propellant chemicals burn, they generate lots of gas very quickly. The gas shoots from the back of the bullet, increasing the pressure behind it, and forcing it down the gun barrel at extremely high speed (300 m/s or 1000 ft/s is typical in a handgun).
The propellant chemicals in a handgun bullet are not designed to explode suddenly, all at once: that would blow the whole gun open and very likely kill the person firing it. Instead, they are supposed to start burning relatively slowly, so the bullet moves off smoothly down the gun. They burn faster as the bullet accelerates down the barrel, giving it a maximum"kicking" force just as it comes out of the end. As the bullet emerges, the whole gun recoils (leaps backward) because of a basic law of physics called "action and reaction" (or Newton's third law of motion ). When the gas from the explosion shoots the bullet forwards with force, the whole gun jolts backwards with an equal force in the opposite direction.

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