Paint Ball Guns use a CO2 or other gas cartridge. These are regulated as dangerous goods.
There is allowance for passengers to carry small CO2 or other gas cartridges in Division 2.2 (without a subrisk) provided that the gas cartridge is no larger than 50mL water capacity. Maximum of 4 cartridges per passenger. Cartridges larger than 50mL water capacity are not permitted in passenger baggage.