CO2 revolvers 

The CO2 revolver does not use any piston, spring or cocking lever, but a cartridge of CO2 for the propulsion of the projectile. These CO2 cartridges can be disposable or rechargeable. Disposable cartridges typically allow about sixty shots while rechargeable versions exceed 150 shots. CO2 is stored in liquid form in these cartridges, known as diabolo, lead or plastic ammunition with aluminum head.
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