Spring Powered: A spring-powered air rifle utilizes a piston and coiled spring inside the chamber. The rifle is cocked, and the spring will be compressed and then decompressed once the trigger is pulled. Gas Piston: A gas piston air gun works the same way as the spring piston gun but utilizes a gas-filled cylinder instead of a coiled spring. Precharged Pneumatic: The precharged pneumatic (PCP) air gun uses high-pressurized air in the chamber as the propellant force to discharge the pellet. Variable Pump: The variable pump gun has a piston and a pressure cylinder in the chamber. When you cock the rifle, the air between the piston and cylinder is compressed. C02: CO2 powered air gun works the same way as a PCP air gun, but it uses carbon dioxide cartridges (CO2) as the power source instead of pressurized gas.