Cartridge Cases: The Most Important Piece of a Bullet

The cases used in modern bullets are truly what make the whole process viable. The case of the cartridge contains the primer, powder, and projectile in one convenient package. The case serves as a convenient way to handle and store the components, it also serves as a way to seal the breech during the firing process. As a firearm is discharged the brass expands slightly to seal the chamber, keeping the hot gases away from the shooter, thereby making the firearm safe for the shooter. The trick in this safety feature is having the case material strong enough to survive the blast but also flexible enough to provide the needed chamber seal for efficiency and safety. Then after all of that the case material must also be resilient to be able to spring away from the chamber walls, and be ejected.

To fit all of these functions into one material is tough but very possible, the most common material is an alloy of 70% Copper and 30% Zinc, this allows for all functions to be completed safely, reliably, and repetitiously. All cartridge cases can be sorted into various categories by head configuration and body shape. While there are various types of cases, bodies and head configurations the main purpose of the cartridge case is to consistently position the cartridge in the chamber.

The biggest category is the body shape, especially since it is mostly visual. There are the bottleneck, straight, and straight tapered. While the majority of modern rifle cartridges are of the bottlenecked design, there are some that still use the other to types of body shapes. Meanwhile every type of body shape can be seen in different types of cartridges for handguns, like the straight tapered case of the 9mm or the straight case of the 40 S&W.

The head type include the rimmed, semi-rimmed, rimless, belted and rebated rim. The rimmed cases were the rule of thumb for many years while the technology for ammunitions was improving. Rimmed cases have a flange at the base of the case that allowed a finger like protrusion to catch that rim and flip the empty case out of the firearm usually with the help of some form of spring. This rim also help limit the amount of forward travel the bullet would make inside the chamber, therefore the headspace or forward travel of the bullet in the chamber was controlled by the thickness of the rim or flange on the case.

Many Semi-rimmed cases are also bottlenecked so the headspace on these type of cartridges are set by the shoulder. While the Semi-rimmed case is less common than the other bullet types it can still be found especially in the custom reloading, or custom wildcat loads. While the rimless cartridge is the most popular the type of cartridge case in use today, it is still not really a 100% rimless case.

The rimless case still has a rim, the difference is that the rim is the same diameter as the case body, therefore making the profile of the case the same diameter throughout its length. This allows for the cartridges to be stacked in a box type magazine better. The rimless cartridges also make the ease of loading possible and are less likely to jam withing the magazine when loading or unloading the magazine. But just like all good things there are exceptions to these also, there are a few cartridges that use a rimless case but are not bottlenecked, like the 9mm or the 40 S&W.

Then there is the old belted cases, these cases have a "belt" of thicker material directly in front of the extraction cannelure. Originally designed by Holland & Holland for the 400/375 Nitro Express, they were designed to withstand the extra power of the Nitro Express. Oddly enough with modern materials and technology the belted cases are now more cosmetic then functional. Since the belted was also used on the "Magnum" cartridges, they became popular wit the magnum cartridge users. Consequently all magnum cartridges that have come to market without a belt have not been as popular as the cartridges with a belt, even though thee functionality of the cartridge was unchanged.

While there are many bullets types out there on the market, it still is said that the best ammunition your firearm will shoot is ammunition that you load yourself. While this may be true, the store bought factory cartridges will serve as a great starting ground for any beginner. The only true advise I have is to not purchase a firearm based on cartridge but on how you feel with the firearm. There will always be a larger than life number of cartridge choices, the best you can do is to try and find the one that best suits you. There are as many different cartridges as there are different people, to test them all would cost an enormous amount of money, the next best thing is research. Cases serve more than just a safety sealant between us and the explosion of gases, they still serve as the revolutionary invention that made cartridges possible, firearm ammunition convenient, and firearms safer for the shooter.