Hi - By GAS I think you mean C02. As far as I know and checking other posts about the internet you should be able to run the BT4 on AIR without any modifications. LIPS and RAP4 sell BT4 Slicer currently with Air tanks. There are also bottom line and flex air kits to convert the location of the tank. So your options are varied. Now is the BT4 a good marker....that's a completely different question which I'm not qualified to answer as I've never had one. I'm sure other owners of BT4's could chip in.