A certain amount of energy is required to push a bullet out of the cartridge case, through the barrel of the gun and out to the target. This energy is created from the gunpowder stored inside the cartridge case.
Gunpowder is a chemical compound that, when ignited by a spark, burns very rapidly and produces a relatively large volume of hot, expanding gas. It is this expanding gas that pushes the bullet down the gun barrel and out the muzzle. The earliest form of gunpowder is called black powder and it was invented by the Chinese around 1,000 AD. Black powder is still used today in muzzle loading firearms. Black powder is quite dirty to shoot, and is also corrosive. Black powder firearms have to be cleaned at the end of each shooting session to avoid damage to the bore (the inside of the barrel).
Modern gunpowder is classified as a propellant and is much less corrosive, much cleaner than black powder and burns with much less smoke than black powder. However, guns that shoot modern smokeless powder still need to be cleaned after shooting of the burned gunpowder residue that builds up on the firearms. Today, almost all cartridges are loaded with modern, smokeless gunpowder. Modern gunpowder was first developed in the second half of the 1800s.
The fourth and final component of a round of modern cartridge ammunition is the Primer. The primer is a pressure-sensitive chemical compound that provides the spark that starts the gunpowder burning. The primer compound is similar to a child’s toy cap pistol. When the cap is struck, it goes bang with a tiny flash of flame. The primer in a cartridge acts the same way when the hammer or firing pin of the gun strikes it and produces a tiny flash of flame that ignites the gunpowder inside the cartridge case and pushes the bullet down the barrel and out to the target.
The bullet is the projectile that is fired from rifles and pistols. Typically, shotguns do not fire bullets, they fire multiple small lead spheres called shot. However, shotguns can also fire a single projectile made of lead or copper, called a slug.
Pistol and rifle bullets are designed to fit snugly inside the pistol or rifle barrel. They are made to fit the inside diameter of the barrel, which is called the bore. The Europeans measure the inside diameter of a rifle or pistol barrel in millimeters. For example, the nine millimeter Parabellum pistol cartridge has a bullet of 9mm diameter. Cartridges which were designed in the USA are measured in 100ths and thousandths of an inch, such as the 357 Magnum cartridge, which has a diameter of 0.357 inch.
Shotgun barrels are different. For example, a 12 gauge shotgun barrel is based on the diameter of a spherical lead ball that fits snugly into the barrel. The number of lead balls of that size that make up a weight of one pound (in this example, 12) determines the gauge of the barrel. The internal diameter of a 12 gauge shotgun barrel is equal to the diameter of a lead ball weighing 1/12 pound, which is 0.729 inch. A 20 Gauge shotgun has a barrel of 0.615 inch and it takes 20 lead balls of that diameter to equal one pound in weight.
Most pistol and rifle bullets are made either entirely from lead or have a lead core that is covered with a copper jacket. If the lead is covered by the copper jacket, the barrel tends to stay cleaner (and needs less frequent cleaning) than if lead slugs are fired. A bullet with a hole drilled in the front is a hollow point bullet. The bullet is more likely to deform and create a larger hole when it hits living tissue such as an animal or criminal.
Such bullets may be described as full metal jacket, semi-jacketed or semi-jacketed hollow point, depending on the extent of the copper jacket over the lead core.
Today, we commemorate the adoption of the Declaration of Independence on July 4, 1776, by the Continental Congress declaring that the thirteen American colonies regarded themselves as a new nation, the United States of America, and no longer part of the British Empire.
Happy Birthday America!