Which component of the bullet is primarily responsible for launching it from the firearm?

The component of the bullet primarily responsible for launching it from the firearm is the powder. When the trigger is pulled, the firing pin strikes the primer, igniting it. This ignition then creates a rapid expansion of gas through the burning of the powder, which generates the force needed to propel the bullet down the barrel and out of the firearm.

The other components have important roles but do not actively launch the bullet. The bullet itself is the projective part and is propelled by the force of the expanding gases. The casing holds all the components together but does not contribute to the launching process. The primer serves to initiate the combustion of the powder but is not responsible for producing the gas needed for the launch. Therefore, the powder is the critical element in the system that provides the energy necessary to fire the bullet.