If there is not an adjustment built directly built into the gun, then it would be illegal to do so in the United States.
For an air/piston powered .177 BB gun - anything less than 200 feet per second (fps) For a CO2 powered BB gun - anything less than 300 fps. For an "AIR SOFT" gun - anything less than 150 fps.
It depends on the KGS system, and the FPS of it the gun.
All Co2 tanks will fit any gun meant to be powered by Co2.
No
Read the directions for YOUR gun. CO2 does not explode, but may leak down.
The fps depends on the brand and quality of the gun. If the gun is high powered spring it is probably at most 350 fps. Most likely the gun is less then this in the 275-315 range.
On the model I have,the fps screw is located towards the back of the gun under the bolt
CO2 powered weapons are usually fitted with a removable cartridge - which is stored in the handle of the gun.
A Co2 gun can go up to 300 fps. Sling shoots only get a paintball up to 240.
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.
Define real? If you mean like a actual gun which shoots bullets, no. If you mean real as in not fiction, yes. There are several CO2 powered rifles, such as the Beretta CX-4 Storm which is powered by a 88 gram CO2 cartridge.