Cartridge Cases are usually made of brass, a composition of 70% copper and 30% zinc.Less commonly,they are made of steel of aluminum,zinc and plastic materials that have been used experimentally.Brass,plastic and paper are used for shot-shell tubes.The main function of the cartridge case is to expand and seal the chamber against the rearward escape of gases when the cartridge is fired.When a brass cartridge is fired in a weapon,the gas pressure produced by the burning of the propellant expands the case tightly against the walls of the chamber.If the brass is tempered to the correct hardness,it will spring back to approximately its original dimensions and make the case easy to extract.If the brass is too soft,it will not spring back and will make extraction difficult.If the brass is too hard,that is,brittle,it will crack.
_ There are three general shapes for cartridge cases: 1. Straight 2. Bottleneck 3. Tapered Almost all pistol cartridges are straight whereas almost all rifle cartridges are bottle-necked.The
bottle-necked design permits more powder to be packed in shorter,fatter
cartridge than would be possible in a straight cartridge where the
lumen is approximately the diameter of the bullet.Cartridges with
tapered cases are virtually obsolete.
_Cartridge cases are classified into five types according to the configuration of their bases. 1. Rimmed (e) 2. Semi-rimmed (d) 3. Rimless (c) 4. Rebated (b) 5. Belted (a)
_Rimmed cartridge cases have
an extractor flange that is larger than the diameter of the cartridge
case body.The letter R is added after case length numbers in the metric
system of caliber designation.
Semi-rimmed cartridge cases
have an extractor flange that is larger in diameter than the cartridge
case body,but they also have a groove around the case body just in front
of the flange.The metric designation for these cartridges is SR.
Rimless cartridge cases
have an extractor flange whose diameter is the same as that of the
cartridge case body and also have a groove around the body of the case
in front of the flange.In the metric system of caliber designation,no
letter is used for this type of cartridge case.
Rebated cartridge cases has
an extractor flange that is smaller than the diameter of the case.A
groove around the body of the case is present in front of the flange.The
metric designation is RB.
Belted cartridge cases
has a pronounced ,raised belt encircling the cartridge case body in
front of the groove in the body.The diameter of the extractor flange is
immaterial.The metric designation is B.