A shell is a small tool. It holds many tiny bits. These bits fly out. The shell helps them move. It is used for many jobs. 
A shell is a small tool. 

Most shells have a plastic tube. A metal base is at the bottom. Inside, there is powder. The powder makes a push. This push sends the bits out. 
A small part called a wad is inside. The wad keeps the powder and bits apart. It also helps the bits move well. It acts like a seal.
Some shells have one big piece. This is called a slug. Most shells have many tiny bits. These bits are called shot.
People use different sizes of shells. The size is called a gauge. A 12-gauge is very common. Small shells are also used.
A shotgun cartridge is a tool used in shotguns. 

A shell has several parts. It usually has a plastic hull, which is the main tube. At the bottom is a metal base. This base holds a primer. The primer starts the push. Inside the tube is propellant. This is the powder that makes the shell work.
A part called a wad sits inside. The wad keeps the powder and the shot separate. It also acts as a seal. This seal stops gas from escaping the wrong way. 
Shells come in different sizes. This size is called a gauge. A 12-gauge is the most popular size. A 10-gauge shell is bigger than a 12-gauge. Smaller shells include the 20-gauge. There is also a very small size called .410 bore. 
A shotgun cartridge is a special type of ammunition. It is a cylindrical tube used only in shotguns. 

Inside the shell, several parts work together in a specific way. First, the primer at the base starts the process. This ignites the propellant, which is the powder inside. 
People have changed how shells are made over a long time. Early cartridges used brass cases, much like rifle ammunition. In the late 1870s, makers began using paper hulls instead. These paper shells were popular for almost one hundred years. By the early 1960s, paper was replaced by plastic hulls. By the early 1980s, plastic hulls were used everywhere. 
Shell sizes are measured by a term called gauge. This measurement comes from an old UK law from 1885. A 12-gauge is the most popular size used today. Interestingly, a 10-gauge is actually larger than a 12-gauge. A 20-gauge is smaller than a 12-gauge. There is also a very small size called .410 bore. 
You can think of a shotgun shell like a small engine. The powder is the fuel that provides the push. The wad is like a gasket that keeps everything tight. 
A shotgun cartridge, also known as a shotshell or shell, is a specialized type of ammunition. It is a cylindrical, rimmed container designed specifically for use in shotguns. 
Modern cartridges follow a precise mechanical sequence to function. The process begins at the base of the cartridge with the primer. When struck, the primer ignites the propellant, which is the chemical powder inside the shell. 

Cartridges are categorized by different types of projectiles and materials. Traditional shot is often made of lead, but many modern versions use steel, tungsten, or bismuth. These alternative metals are used due to environmental restrictions on lead or to achieve higher velocities. There are also specialty projectiles like rubber balls, rock salt, and magnesium shards. Some cartridges are even designed as non-lethal rounds, such as bean bag rounds. 
The materials used to build the cartridge hull have changed significantly over time. Early shotgun cartridges used brass cases, which looked very similar to large rifle cartridges. In the late 1870s, manufacturers began replacing brass with paper hulls. These paper shells remained the standard for nearly a century. During this era, makers used various materials for wadding, such as felt, leather, cork, or paperboard. Starting in the early 1960s, plastic hulls began to replace paper. By the early 1980s, plastic hulls had become the universal standard for most cartridges. 
Understanding shotgun size requires understanding the concept of "gauge." Unlike rifles, which use "caliber" to measure internal diameter, shotgun size is based on a historical definition. This definition is tied to a UK law from 1885. Theoretically, the gauge is based on the diameter of a lead ball that weighs a specific amount. For example, a 12-gauge shotgun is sized so that a lead sphere fitting the barrel weighs 1/12th of a pound. Because of this math, a 10-gauge barrel is larger than a 12-gauge barrel. Similarly, a 20-gauge barrel is smaller than a 12-gauge. 

Different gauges serve different practical purposes. The 12-gauge is the most popular choice worldwide. The larger 10-gauge was once used for hunting large birds like turkey, though it is now less common because modern 12-gauge "magnum" loads offer similar power. The 20-gauge is a popular mid-size option. It is favored by smaller shooters because it has less recoil. It is also used by experienced target shooters who enjoy the challenge of a smaller shot charge. Other gauges, like the 16 and 28, are also commercially available, while older sizes like the 4 or 8 gauge are now mostly collector items.
Specialized ammunition exists for very specific environments. "Snake shot," also called birdshot or ratshot, consists of very small pellets. This type of ammunition is often used in small handguns or "garden guns." 
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