Firearm ammunition and its construction is a vast, specialized part of the firearms world. Different ammunition exists for different purposes and is optimized for maximum performance in different areas. Precision target shooters use ammunition specifically designed for maximum accuracy out of a single rifle, while police departments use ammunition designed to stop a threat as quickly as possible. Despite this large variety in purposes, all ammunition has components that are common across all these variations.
The main component of any round of ammunition is the case. Cases are usually made of bare brass, although steel cases are also used in some instances (usually foreign military surplus ammunition) and some higher-end pistol ammo uses nickel-plated brass. Cases are tubular, with one closed end, and are the housing into which the remaining ammunition components are installed. A single completed piece of ammunition is referred to as a "cartridge" or a "round".
Bullets are the ammunition component that actually leaves the gun when fired, traveling down the barrel and through the air to the target. Almost all bullets are made from lead and have a copper jacket bonded to the lead core. Many specialty bullets exist, such as long distance target bullets, hunting bullets with a soft nose for expansion and quick killing, or even bullets with a steel core for piercing armor plating. Bullets are press-fit into the open mouth of a case.
Gunpowder is the driving force behind a bullet. Every round of ammunition has a quantity of gunpowder inside the case which explodes when ignited and forces the bullet downrange. The burn speed and volume of powder used is specifically tailored to the weight of the bullet being fired, the type of gun it is being fired out of, and the desired bullet velocity. Using the wrong kind of powder, or too much of it, can result in catastrophic damage to the gun and sometimes to the person firing it. Ammunition manufacturers and hand loaders go to great lengths to ensure their powder selections are appropriate and safe.
Primers are the last key component of firearms ammunition. In order to set fire to the gunpowder inside a case, a reliable spark must be supplied. Primers are tiny percussion explosives that flash a hot stream of sparks and create concussive pressure when struck by a gun's firing pin. They fit into a small pocket on the closed end of an ammunition case. If you look at a round of ammunition, the primer is the small silver circle on the end opposite the bullet. Fired cases will have a dent in the primer where the firing pin struck and caused ignition.
- "ABC's of Reloading"; C. Rodney James; 1997
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