What component is responsible for propelling a bullet out of the barrel?

The component responsible for propelling a bullet out of the barrel is the propellant, which generates expanding gases upon ignition. When a cartridge is fired, the primer ignites the propellant, and this combustion produces a large volume of gas very rapidly. The rapid expansion of these gases creates a significant amount of pressure in the chamber of the firearm. This high-pressure gas forces the bullet out of the casing and down the barrel at high speed.

Understanding the role of propellants is crucial in firearms operation, as they are what enables the projectile to achieve the necessary velocity for effective range and impact. Other factors such as gravity or friction do play roles in the bullet's trajectory and movement through the barrel but are not responsible for the initial propulsion. The mechanical action of the hammer is also important for firing the round but does not propel the bullet itself; it's the propellant that provides the necessary thrust after ignition.