Buffer spring is a spring which gives elasticity to a buffer, so as to lessen the shock of collision. Buffer springs provide a very simple yet important purpose in a rifle. Each time the gun is cocked or a round is fired the bolt carrier has to follow through an action to load a round into the chamber. When the bolt carrier is either cocked back or pushed back it hits the buffer and buffer spring inside the buffer tube. This action pushes the bolt carrier forward to pick up a round.