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.
They all work the same. All spring-piston guns have a spring-powered piston (some have more than one) inside a compression chamber. That chamber connects to the barrel through an air transfer port. When the gun is cocked, the piston is withdrawn into the compression chamber, and air is drawn through the transfer port.