No
Usually, the only non electric rifle this is also automatic will be CO2 powered.
If there is not an adjustment built directly built into the gun, then it would be illegal to do so in the United States.
All Co2 tanks will fit any gun meant to be powered by Co2.
A paintball gun needs CO2 (or HPA) to fire at all.
Read the directions for YOUR gun. CO2 does not explode, but may leak down.
No you do not need to put air in an airsoft gun. These guns are either spring powered where you must cock the gun before you shoot it, electric powered which are automatic and require batteries, or CO2 powered which requires a CO2 cartridge. This CO2 is not expensive and a pack of 40 CO2 cartridges costs only 20-25 dollars. the guns that require CO2 are not as common as the other forms of airsoft guns, although they are more powerful. In general, if you buy an airsoft gun, you do not need to put any air into it.
CO2 powered weapons are usually fitted with a removable cartridge - which is stored in the handle of the gun.
Richard Gatling invented the Gatling Gun in 1861. The first self-loading rapid fire gun was the first modern automatic weapon. Sir Hiram Maxim developed the first self-powered or recoil powered automatic gun in 1885 with the Maxim Gun.
In the truest sense of the definition of "automatic", no a bb gun cannot be automatic. In function, however, a BB gun can be automatic. A good example would be the Drozd BB gun which fires full automatic, but used CO2 as the power source.
In airsoft guns, automatic electric gun. Battery powered airsoft, versus spring powered or gas powered.
An air-soft gun that is powered by CO2 or green or red gas instead of a spring or a battery.
Pain is different for each person. But in general, CO2 Powered would be more painful. Because of the constant speed of it in general.