Dual Fuel Compressed Air / CO2 Air Rifle Trouble-free, highly accurate. Once it is filled, there is no pumping and no worry about the outdoor temperature. Just shoot until the gun needs to be refilled. The Discovery's 2000 psi fill level means almost anyone old enough to shoot this rifle will also be able to fill it from the hand pump that comes in the package. Dual Fuel - An inexpensive CO2 adapter converts this rifle from compressed air to CO2 operation which makes it easy to fill from a standard paintball tank, offering more shots from a single fill. CO2 is excellent for indoor use or for outdoor casual plinking.