here's some interesting info...
(this is general information assuming you have a 200-230bar dive cylinder...)
''...when you hook your empty bottle up to a scuba tank containing 3000 psi, then open the valve, the two tanks equalize together, taking some of the air from the scuba tank. Each time you equalize into your paintball tank, you lose about 200 psi from the scuba tank. So your first fill will be about 2800 psi, your second will be about 2600 psi, the third will be about 2400 psi, etc...''
the less air you get per fill, the more chance of starving your marker and getting drop off, especially with a gas hungry gat.
conclusion - get yourself a 300bar dive cylinder, the bigger the better...
shots per cylinder calculator -
http://www.scubatoys.com/paintball/paintballshots.asp
scuba tank/paintball cylinder fill calculator -
http://www.scubatoys.com/paintball/scubafills2.asp
hope this help's someone...