What is a gun? How does it work?

A gun is a weapon that uses the force of an explosive propellant to project a missile.
Guns or firearms are classified by the diameter of the barrel opening. This is known as the caliber of the gun. Anything with a caliber up to and including .60 caliber (0.6 inches) is known as a firearm.

When the trigger is pulled the hammer hits the firing pin. The firing pin then hits the primer which causes the powder to burn hence producing lots of gases. This causes the volume behind the bullet to fill with extremely high pressure gas. The gas pushes on every surface it encounters, including the bullet in front of it and the base of the gun barrel behind it. The increase in pressure caused by the gases causes the bullet to be forced into the barrel hence causing the bullet to come out the muzzle at very high speeds. Once the bullet is fired, it remains in motion from its momentum. The momentum will carry the bullet until it strikes an object or gravity pulls the bullet towards the earth.

Firearms change potential chemical energy into kinetic energy in the actual firing of the gun. Many people do not realize that the force imparted by accelerating the bullet is not the only force acting on the gun, or the shooter. Grains of burned gun powder are sent out the muzzle at high velocity. When the trigger is pulled, the hammer strikes a small charge at the end of the shell, the ammunition. This charge ignites black gun powder packed behind the lead ball bearings. When the black gun powder burns, it produces gas that rapidly expands with the burning of blacker gun powder. High pressure gases exert forces on the back of the bullet and on the gun. The only way for the gas to escape is to push the bullet out of its way through the end of the barrel. This is how a bullet is fired from a gun.

The conservation of momentum is also demonstrated when the bullet hits an object. The object that it strikes absorbs the kinetic energy, energy from motion and momentum. If the force of momentum from the bullet is great enough to overcome the mass of the object, the target will be moved along the same vector as the bullet.

To increase the accuracy of the flight of the bullet, a technique called rifling can be used. Rifling is where the barrel of the gun and or the bullet is creased with spiral grooves that allow air to pass through. When the bullet is fired, the air passes through these curved grooves and spins the bullet. This spinning action allows the bullet to cut through the air more efficiently and fly on a truer course, thus stabilizing its trajectory.