Internal Ballistics http://www.esm.psu.edu/courses/emch12/intdyn/activities/kinetics_particle/ballistic/images/antique-gun.jpg The internal ballistics occur entirely within the firearm. The propulsion of the bullet all begins within the chamber of the gun as the propellant ignites. This explosion creates an enormous amount of pressure behind the bullet, giving the bullet its kinetic energy. The recoil typically associated with firing a gun comes as a result of Newton's Third Law, that every reaction has an opposite reaction. As the bullet is forced out of the barrel there is an equal force pushing the firearm back toward the person holding it.