In the Western world, these are almost invariably made of brass with a 75 : 25 copper/zinc alloy. Other materials including steel and plastic have been used, but not on any commercial basis.
Aluminium-cased pistol ammunition has recently acquired some commercial success due to the cost saving of aluminium over brass. There are, however, a number of disadvantages. These include being non-reloadable and less robust than their brass counterparts. For large-scale users who do not wish to reload their empty cartridge cases or are firing for purely training purposes, the savings can, however, be very considerable and far outweigh the disadvantages.
In modern ammunition from Russia, Warsaw Pact countries and China, the cartridge cases are invariably made of steel. In China, the steel is coated with copper to prevent rusting whilst elsewhere, it has a heavy green/grey coat of lacquer for the same reason. In World War II, due to a shortage of raw materials, a number of countries, notably Germany and Russia, used lacquered steel cartridge cases as well. These are still encountered.
Shotgun cartridges generally have a brass base with a plastic, or sometimes paper, case. All-plastic shotgun cartridges have been produced, but they have not proved to be a commercial success.
The main purpose of the cartridge case, other than for holding the components together, is to expand and seal the chamber during firing. This is called 'obturation' and prevents the explosive escape of high-pressure gases through the breech. During manufacture, the brass is annealed to give the case the correct degree of hardness. If this is correct, the brass will regain its original shape after the pressure has subsided and the case will be easy to extract from the chamber.
If it is too hard, the case will crack, and if too soft, it will cling to the chamber walls and be extremely difficult to remove.
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