A review on the physiology of Insulin like Growth Factor-I (IGF-I) ... by Debnath, Surajit / Advances in Environmental Biology.
The spring piston airgun generates power using a powerful spring-loaded piston that is housed within a compression chamber. Cocking the gun (using a break barrel, side lever, or under lever mechanism) causes the piston assembly to compress the spring. When the spring is released it pushes the piston forward compressing a column of air in the chamber behind the pellet.
Spring-powered airsoft guns are single-shot devices that use elastic potential energy (EPE) stored in a spring to compress air to launch an airsoft pellet down the barrel of the gun. The user must cock a spring gun prior to each shot.