Shotgun cartridges consist of a number of components:
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Brass head with rim. The rim stops the cartridge sliding too far into the chamber at the end of the barrel. It also enables the ejection mechanism to eject the cartridge when the shotgun is broken (OU and SS shotguns) or after the shot is taken (SA).
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Primer inside the brass head. This contains a small amount of explosive which, when struck by the hammer or firing pin of the shotgun, ignites the powder.
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Case. These days this is usually plastic, in the past it was cardboard or compressed paper. The case is crimped at the end to hold the pellets in place.
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Powder. This does not explode but, when ignited by the primer, burns very quickly and it is the expanding gas generated by this burning that forces the wad and the pellets along the barrel.
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Wad. This separates the powder from the pellets. In many modern cartridges the wad is a plastic cup which is designed to absorb some of the initial shock as the powder ignites and then to hold the pellets together as they travel up the barrel. The plastic wad is designed to stop the pellets deforming before they leave the barrel.
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Pellets (or “shot”). These may be of different sizes and are referred to by number or diameter. For example, number 7 shot is smaller than number 6 shot which is smaller than number 5 shot etc.
A cartridge is defined by its gauge (see below), by the weight of pellets (in grams or ounces) and the size of pellets. For example: “12g, 29g No 9” or “12g, 1 1/8oz, No 7.5”
Plastic wads are a technological solution to the problem of pellets deforming as the powder burns and as they are forced along the barrel.
The problem is that plastic wads are not normally bio-degradable, they can remain on the surface of the ground of decades or even hundreds of years. This may not be a problem on a fully contained shooting range which can be periodically cleaned but it is a problem when shooting game or when clay shooting takes place in an area that will be used for livestock.
Fibre wads are the traditional way of separating the powder from the pellets and they have come back into favour because of their greater eco-friendliness.
The same can be said of pellets which have traditionally been made of lead – a poisonous material which can damage animals (and humans) if ingested. Steel shot, or bizmuth shot, is now a requirement when shooting ducks and may be a requirement on shooting grounds where livestock or wild animals may be in danger.
