What is a firearm ?
A firearm in its most basic form is a hollow cylinder that is closed on one end that contains a propellant charge with a projectile seated on top of the charge. When the propellant is ignited, a large volume of gas is created at high pressure. The gas in an effort to equalize itself with the outer atmosphere seeks the path of least resistance, pushing the projectile out of the barrel and hopefully hitting the target.
Firearms Types
There are three basic groups of modern firearms; shotguns, rifles and handguns.
Shotguns
Shotguns are shoulder fired smoothbore firearms designed to fire cartridges containing multiple projectiles (shot). They may also use ammunition containing a single projectile called a slug. From a hunting standpoint, shotguns have a relatively short useful range of less than 50 yards (45 meters) and the muzzle velocity will be between 1100- 1400 feet per second (335-426 Meters per second) for birdshot or buckshot and 1500 to 1600 fps for slugs . The larger the shot size used the greater the target penetration that there will be at a given distance and muzzle velocity. 12 Gauge is by far the most common gauge used in the U.S.A with the 20 gauge a distant second.
Rifles
Rifles are shouldered fired firearms with barrels having two or more spiral groves in to which the bullet will press as it travels down the barrel. This imparts a gyroscopic spin, which will help stabilize the projectile after it leaves the barrel. There are various categories of rifles. Some rifles fire handgun cartridges such as carbines and submachine guns while others will use more powerful bottleneck cartridges. High-power rifles such as those that are used for hunting big game will fire high velocity bullets generally with a high sectional density. Intermediate cartridges are military cartridges using smaller cartridge cases and smaller projectiles than high power rifles. The most common cartridges of this type are the NATO 5.56mm and the 7.62 x 39mm Russian.
Handguns
Handguns are short range firearms with short rifled barrels that may be held and fired with one hand. They generally fire a bullet with a rounded nose at velocities of between 600 - 1400 feet per second(183-426 meters per second). The two main types of handguns are the revolver and the semiauto pistol although there are a number of other types.
The Self Contained Cartridge
In use for over 150 years, the self contained cartridge has 4 major components; a cartridge case,a primer,a propellant charge and the projectile.
Components of Modern Self Contained Cartridges
Cartridge Case
The cartridge case serves two purposes, first it acts as a gas seal to prevent the powder gases from exiting the rear of the firearm, second it serves to hold the cartridge components together and in the right position for the proper operation of the firearm.
Cartridge cases have been made from a variety of materials such as brass, aluminum, steel, plastic, paper, zinc.
Modern shotshells are made of plastic with a steel or brass case head. Rifle and handgun cases generally made from brass although you may encounter cases made from steel or aluminum. From a reloading standpoint, only brass cases are used.
Primer
The purpose of the primer is set off the main powder charge. When the firing pin or hammer strikes the primer an impact sensitive compound contained in it is compressed between two hard metal surfaces the primer cup and a device called an anvil. This sudden compression causes the priming compound to detonate, creating a momentary flame to ignite the powder.
Rimfire ammunition has a folded rim which contains a primer compound. When the firing pin strikes the edge of the cartridge case, the priming material is compressed rim causing the primer to detonate and ignite the powder. Rimfire cases are not practical to reload and are generally so inexpensive that they are not worth reloading.
There are two basic types of centerfire primers in use today, Berdan and Boxer primers. Berdan primers are essentially small metal cups containing priming compound. The anvil is part of cartridge case itself. Berdan primed cases will have two small flash holes offset fromt the center of the cartridge head. With Boxer primers the anvil is in the primer. Boxer primed cases will have single hole through the center of the head of the cartridge case. In terms of function and reliability there is virtually no difference between the two systems.
Smokeless Powder
Smokeless Powder isn't truly smokeless but it is a considerable improvement over blackpowder. Before the advent of smokeless powder battlefields were obscured by huge clouds of gray smoke and riflemen unless they were firing from dense woods were easy to locate by the smoke generated by black powder. It is made primarily of Nitrocellulose also known as Gun Cotton mixed with other additives depending on the application it is designed for.
There are a number of different powders available for different applications, Rifle handgun and shotgun. For civilian use there are two primary types of powder double base and single base. Single base Smokeless powders are primarily composed of Nitrocellulose and are used mostly for High power rifle cartridges with large volume cases. There are however a few newer fast burning single base powders designed for loading pistol and shotgun cartridges. Double based powders are also made of Nitrocellulose with some quantity of nitroglycerin added. Powders with higher concentrations of nitroglycerin are faster burning and are generally used in shotgun and pistol ammunition. Powders used for shotguns usually may also have pistol applications And vice versa. Rifle powders are generally slower burning and operated at much higher pressures.
An interesting bit of trivia is that nitrocellulose was one of the first commonly available plastics. It was used to make many household items and in the early days of movie production to make film stock. Many studios and movie theatres have burnt down in the early part of the 20th century due to careless smoking around nitrocellose based film.
Projectiles
For high power, high velocity rifle cartridges, jacketed bullets are most frequently used. Pistol and revolver bullets may be jacketed or all lead.
Most modern shotgun loads will use a one piece plastic wad-column or cup wad containing a measured amount of lead or steel shot.