Generally, modern ammunition comes in two variants, the centerfire cartridge and the rimfire cartridge. Most ammunition today are center fire which make it the most common. The centerfire cartridge has its primer located in the center of the cartridge. The primer is separate and can be replaced unlike rimfire cartridges that need to be crushed upon impact by the firing pin. This means that it is reloadable while the rimfire cartridge is not. The centerfire cartridge is made up of four basic components; the case, the primer, the propellant and the projectile.
The case or shell: this is that object that pops out through the top of the gun and drops to the floor after the bullet pops out. The case of a centerfire cartridge is the container that houses the other components. It also has a segment-like structure which prevents friction between the other components. The last thing you want is your firearm going off before you pull the trigger. So, the case performs a parent role by preventing this. The case is made of either brass, steel or aluminum. Most centerfire cases are made of brass because the steel can endure repeated use without having cracks or being damaged. Though, the centerfire cartridge can be used repeatedly, it is not advised to use a particular cartridge more than 5 or 6 times.
The Primer: this is the standout feature that distinguishes a centerfire from a rimfire cartridge. It ignites when struck by the firing pin. The contact of the firing pin on the primer causes it to light up and burn the powder through the “flash hole”. The powder turns into gas rapidly and forces the projectile out of the gun barrel. This whole process which happens rapidly, all starts with the firing pin and the primer. The primer in the centerfire cartridge is located at the center of the case.
The Propellant: this is most of the time smokeless gunpowder. It burns at a very fast rate. The burning powder turns into highly pressured gas which pushes the bullet or projectile out of the case and through the gun barrel.
The Projectile: this could be any object built to be fired via a gun. The bullet is mounted at the top of the casing. Most times, it is a small pointed object made of lead known as a bullet. This little object which might vary in size and length is forced out of the cartridge. It goes through the barrel and flies towards the target at an impressive speed that can go over 2000mph.
The 9mm, .38 special, .45 ACP, .223 Remington and basically all handguns are examples of firearms with the centerfire feature.