Without the metallic cartridge case, self-contained cartridges could not exist. We would still be in the cap-and-ball era. It was the metallic case that made it possible to contain the components—primer, powder and bullet—as one unit within a single cartridge. We evolved from muzzleloading firearms, where each component had to be inserted down the barrel at the muzzle end, one at a time, with the assistance of a ramrod to seat each of these components into place. This process could take up to or over a minute to load, for the resulting one shot. Once the trigger was pulled and the firearm discharged, this entire process had to be repeated so another round could be fired. The self-contained cartridge allows the shooter to very quickly load each round into a firearm. This led to the development of speedloaders and clips to load all the rounds the firearm could hold in its magazine, with one swift motion by the shooter.
The two types of metallic cartridge case body shapes are bottleneck cases and straight cases, also known as straight-wall cartridges. The bottleneck cartridge got its name because it looks like a soft drink bottle. These cartridges, from top to bottom, have a neck, shoulder, body and a primer pocket.
The second type of metallic cartridge case is the straight or straight wall. There are two types of straight cases. The first type is the same diameter from the case mouth to the entire length of the cartridge. The second type is the tapered case, in which the case mouth is smaller than the bottom of the case body. In some calibers, this taper can be hardly noticeable while others have very sharp tapers.
Metallic cartridge cases are categorized by the type of case head it has. The case head is located at the bottom of the cartridge where the primer is located, and where the cartridge identifiers are located such as caliber and manufacturer information. The case head is also a crucial part of the extracting system of the firearm. The extractor groove is found just forward of the case head or cartridge rim. There are five types of case heads by which metallic cartridges are identified: rimless, rimmed, belted, semi-rimmed and rebated.
Rimless
Rimless cartridges are usually used in semi-automatic pistols. The rimless case cartridge has a case head the same diameter as the body of the cartridge. An imaginary line drawn from the body of the cartridge to the case head would be a straight line.
Rimless cartridges are considered more reliable than other cartridges, and are also considered to work more smoothly in the loading, firing and ejection than other cartridges.
Rimmed
Rimmed cartridges are usually found on early or older developed rounds, like the .38 Special and the .30-30 Win. The rimmed cartridge is sometimes referred to as a flanged cartridge.
The rim on a rimmed cartridge is very pronounced, being much larger than the case body. It is this rim that holds the cartridge in the cylinder of a revolver or the back of the chamber. Rimmed cartridges are not found in semi-automatic firearms because their design is not conducive to operation in magazines.
Belted
Belted cartridges are usually found on larger magnum calibers in big-game rifles. If you grew up in the late 1970s and 1980s reading hunting articles by Jack O’Connor, Elmer Keith or Robert Ruark you have a special affection for belted cartridges. These rounds were often referred to as the “sexy” cartridges.
Belted cartridges have a pronounced “belt” around the base of the case body just forward the extractor groove. The belt is designed to reinforce the body ahead of the head case. It also serves as the component of the cartridge to set the proper head space.
Semi-rimmed
Semi-rimmed cartridges have a rim that is only slightly larger than the case body. Unlike a rimmed cartridge, which has a very pronounced rim, the semi-rimmed cartridge solved the problem that rimmed cartridges had in box magazines. Semi-rimmed cartridges can easily be fed from the magazine of a firearm into the chamber.
Many larger caliber rifles have corresponding semi-rimmed rounds for using bolt-action rifles when hunting dangerous game. Semi-rimmed cartridges can be found in calibers ranging from .25 ACP to .444 Marlin.
Rebated
Rebated cartridges have a noticeably smaller rim compared to the case body of the cartridge. The purpose of the rebated cartridge is to get more rounds into a firearm’s magazine. The purpose of the rebated rim is for extraction of the spent or live cartridge.
Rebated rims are usually found in straight wall cartridges. Rebated rim cartridges are usually larger calibers. It also allows for some smaller caliber firearms to be easily converted to larger rebated cartridges.
As shooters, we should always strive to become educated about our firearms and ammunition. This means learning the parts and the correct terminology that goes along with it. It is the cartridge that the whole firearm is built around. The metallic cartridge dimensions of length, angles and circumference determine how the chamber is milled out. The caliber determines the twist rate of the barrel. Additionally, the case design determines the headspace of the chamber.
The cartridge can tell the shooter a lot about its intended use and how it is used. The cartridge can tell you if it is a small, medium or large game round. The case head can indicate if it is commonly used in a revolver or semi-automatic handgun. Since the cartridge is so important for the firearm’s design, the type of action, and what it is used for, it is important to be able to identify the parts and name of each of them. Remember, the metallic case cartridge is one of the most important components of a firearm that is not part of the gun!
