Shotgun Shell - Construction of A Typical Shotshell

Construction of A Typical Shotshell

Modern shotgun cartridges typically consist of a plastic case, with the base covered in a thin brass covering. Paper shells used to be common, and are still made, as are solid brass shells. Some companies have produced what appear to be all-plastic shells, although in these there is a small metal ring cast into the rim of the shell to provide strength. Often the more powerful loads will use "high brass" shells, with the brass extended up further along the sides of the shell, while light loads will use "low brass" shells. The brass does not actually provide a significant amount of strength, but the difference in appearance provides shooters with a way to quickly differentiate between high and low powered ammunition.

The base of the shotshell is fairly thick to hold the large shotgun primer, which is quite a bit longer than primers used for rifle and pistol ammunition. Modern smokeless powders are far more efficient than the original black powder used in shotgun shells, so very little space is actually taken by powder; shotguns use small quantities of powerful double base powders, equivalent to quick-burning pistol powders, with up to 50% nitroglycerin. After the powder comes the wadding. The primary purpose of a wad is to provide a gas seal, since without a wad the gas would just blow through the shot rather than propelling it. The wad consists of three parts, the powder wad, the cushion, and the shot cup, which may be separate pieces or be one part. The powder wad acts as the gas seal (known as obturation), and is placed firmly over the powder; it may be a paper or plastic part. The cushion comes next, and it is designed to compress under pressure, to act as a shock absorber and minimize the deformation of the shot; it also serves to take up as much space as is needed between the powder wad and the shot. Cushions are almost universally made of plastic with crumple zones, although for game shooting in areas grazed by farm stock or wildlife biodegradable fibre wads are often preferred. The shot cup is the last part of the shell, and it serves to hold the shot together as it moves down the barrel. Shot cups have slits on the sides so that they peel open after leaving the barrel, allowing the shot to continue on in flight undisturbed. Shot cups, where used, are also almost universally plastic. The shot fills the shot cup (which must be of the correct length to hold the desired quantity of shot), and the shotgun shell is then crimped, or rolled closed.