Originally Posted by Radarbrew
careful filling those tanks. If you screw it up, you will blow the burst disk (at the least) or freeze the bejeesus outta your fingers. I watched the kid at the paintball place do both on the same day. He lost a bit of skin on his fingers when they defrosted. I suggest a quick lesson from the fill place at a reliable gas filler first.
I would have loved to see that. I used to train the *cough* kids *cough* refs on proper filling. Some of them just couldn't get it though their skulls.
I see one very minor problem with the setup in that link. The tank they are using do not have an on/off knob. I would highly recommend going that route otherwise it could tend to eat o-rings. It is easy enough to swap valves if you have a vice.
You could potentially fill your own 20oz bottle off of a larger one if you have it. Simply do it the old school way. Make a hose adapter that goes between both tanks. Invert the large tank, unless if it has a siphon tube, and turn the knob to fill the smaller tank. As soon as the hissing slows, turn the knob off. As long as you don't freeze the small bottle* before filling there is very little risk of the burst disk blowing. In fact, in 14 years of paintball I've never blown one. Just don't leave a full tank sitting in the sun or in your car (common sense).
*freezing the bottle will give the best fill but do not try this unless if you have a scale handy.