Two identical bullets are fired one by a light rifle and another by a heavy rifle with the same force. Which rifle will hurt the shoulder more and why?

As both the bullets are said to be identical and are fired with the same force, therefore, as per Newton’s third law of motion, every action has an equal and opposite reaction; same force will be applied on both the rifles. As the same amount force is applied on both the rifles, the lighter rifle will move more quickly in the backward direction causing serious injury to the shoulder.