A green gas rig will have the same problem that a CO2 rig will, you'll experience rapid cool-down on full auto.
A compressed air (scuba) rig or a nitrogen rig would work best. You could use a KWC rig if you want, they're available from
www.airsoftpaintballs.com, and that will screw green gas cans onto your gun. Keep in mind your seals will wear out with green gas.
It would be ideal to use a compressed air rig with a low pressure regulator. You should know the ideal operating pressures for your gun, which depends on whether it is stock or not.
-Bart
<img src="http://www.stopstart.fsnet.co.uk/smilie/tooledup.gif" border=0>
Typical airsoft game in Arizona: 11 Arab men in a van with assault rifles.