These airguns have a large warehouse, which accumulates air or CO2 and each time we  pull the trigger vented a quantity of air in the chamber of the gun and the pellet reject.. These air-kick the footloose and highly accurate shot. Is either a shot or repetitive and have highly accurate shots and is usually possible to regulate the energy they produce. Fill the records made by pump or by transference from diving bottle, or even from special air compressor  that is quite expensive.