A standard 20 oz will run for 800-1200 shots depending on the marker.
unscrew the tank, this will vent any co2 that is in the marker out the asa
No, paintball co2 is much higher pressure.
You cant, the CO2 that is in the marker is vented out when you take the tank off.
No paintball gun will work without a CO2 tank or other propellant tank. without Co2 there is nothing to push the ball out of the barrel.
Where the air tank or co2 tank normally attaches
There is no such thing as a "CA" tank.
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CO2, stored in the tank is highly pressurized. The paintball being shot is caused by it being pushed out by the rapidly expanding gas. CO2 also cycles and reloads the next paintball.
Take it to a shop! if you want to do it yourself the normal way is to put the bottle on scales and fill it from a larger bottle to a fill weight. To be honest though CO2 is well out of date. A smart move would be to move onto compressed air.
No I went 4 hours straight on just a 9oz. tank
No, any tank will work.
You cannot unless you have a gauge installed, or know the exact weight of the tank.