 Although the word "bullet" is often used in colloquial language to refer to a cartridge round, a bullet is "not" a cartridge but rather a component of one.A round of ammunition cartridge is a combination package of the bullet (which is the projectile), the case (which holds everything together), the propellant (which provides the majority of the energy to launch the projectile) and the primer (which ignites the propellant).This use of the term "bullet" when intending to describe a cartridge often leads to confusion when the components of a cartridge are specifically referred to.