Which of the following are the four parts of a round?

The four parts of a round, specifically in the context of ammunition, are indeed the projectile, propellant, primer, and case.

The projectile is the actual component that is expelled from the firearm towards the target, often referred to as the bullet. The propellant is the chemical that ignites and produces gas to propel the projectile when ignited. The primer is a small device that, when struck by the firing pin, ignites the propellant. Lastly, the case holds all these components together and provides a seal which helps contain the pressure generated when the propellant burns.

Understanding this structure is essential for anyone involved in handling or maintaining firearms, as each component plays a crucial role in the safe and effective operation of the weapon system.