The Bullet Cartridge
The method of using three separate components (projectile, powder & charge) to fire projectiles continued for hundreds of years until the late 19th century when the first firearm “cartridge” was introduced.
The cartridge was a leap forward in firearm design in that, for the first time the projectile, powder and charge were all contained in one single piece. Often mistakenly referred to as a “bullet”, cartridges use metal casings (usually made of brass) to contain the projectile, the powder and the percussion cap in one weatherproof container. Thus was born the modern bullet cartridge consisting of four components:
- the case or shell (the exterior holding everything together)
- the projectile (bullet)
- the powder (black powder replaced later by smokeless black powder)
- the primer (replacing the percussion cap used to create the spark)
The modern cartridge is the most common type of ammunition used in the world today. See how it functions in a semi-auto pistol below:
Slug vs. Shot
While all cartridges are made up of the same four basic components of case, projectile, powder & charge, there are two primarily different types of cartridges used today with the projectile and case being the elements that define each. Most ammo cartridges contain a single projectile, often referred to as a “slug” or a “bullet”. However, there is a second type of cartridge that fires multiple projectiles which are referred to as “shot”. This, as you can imagine, is where a “shotgun” gets it’s name.
Typical bullet cartridges (also referred to as rounds) are designed for hitting a single target with accuracy being the primary goal. The majority of firearms including pistols, rifles and machine guns all use these types of rounds. Bullets are measured by their physical size which is referred to as “caliber”. Read more about bullet caliber here.
Shot cartridges are often referred to as “shells” or “shotgun shells” and typically contain multiple projectiles with the purpose of spreading the shot over a wide area. The primary purpose for this is hunting where a moving target is often difficult to hit with a single projectile. In most cases today, shotgun shells are made of plastic with a brass backing containing the primer.
Shotgun shells are measured in “gauge”, which is the weight, in fractions of a pound, of a pure lead round ball that is the same diameter as the internal diameter of the barrel. So, a shotgun is called 12 gauge because a lead sphere that just fits the inside diameter of the barrel weighs 1⁄12 of a pound.