Physics of Rifle Shooting Home Introduction Conservation of Momentum Conservation of Energy Bullet Drop Sighting in Bibliography Recoil: Conservation of Momentum After being ignited by the primer, the gunpowder expands and the gasses find the path of least resistance to exit the combustion chamber. The gasses push the bullet out of the casing and down the barrel. According to Newton’s third law of motion, every action has an equal and opposite reaction. This means that as the bullet gets pushed out of the barrel, the rifle must be pushed with equal force in the opposite direction (into your shoulder). According to the law of conservation of momentum, the velocity the rifle moves towards your shoulder is proportional to the velocity and mass of the projectile.   Mass Rifle x Velocity Rifle = Mass Bullet x Velocity Bullet   With this equation you can calculate the velocity the rifle moves into your shoulder. You can further calculate the amount of energy the rifle dissipates into your shoulder with the equation.   KE = ½ Mv2 Certain firearms have a significant amount of recoil, the reaction force from the gases produced by the rifle. http://www.foremosthunting.com/Duck/Tips/DuckHunting101.aspx