The gas consumption of your Shocker has only to do with the fact that it is a Shocker and they are inherently by design less efficient than the Cocker or Angel. Input pressure has nothing at all to do with it. 1.9L bottle should be fine once you switch to a more efficient barrel than the AA that comes with it (notoriously horrid gas gulpers; I threw mine away.) like a CP one piece 14", Armson SSR, or straight bored DYE SS, and getting a bolt tip that has a more open face than the scant 6 hole stock front. (I.e. one that has a greater percentage of the face open rather than the stupid venturi design.)