To fill a paintball bottle you'll need a Co2 fire extinguisher and a fill station similar to this:

http://www.ebay.co.uk/itm/NEW-Paintb...item41570db720

Basically you remove the nozzle from the extinguisher and connect the fill station instead. The paintball bottle is connected to the on/off valve on the fill station. One of ball valves on the fill station is a vent valve, the other is the fill valve. To fill close both valves and then open the extinguisher valve. Slowly open the fill valve, the pressure will also open the pin-valve on the paintball bottle. You have to weigh the amount of Co2 you're putting in the bottle ( they are marked 9,12 20oz etc).

When the weight is right close the fill valve and extinguisher valve, and open the vent valve...then you can disconnect the bottle from the fill station and you'll have a ''full'' bottle.

Best is you get someone who did this before to show you tho, as if not done right you might hurt yourself...we're talking about 50bar here.