The Discovery version is shorter and much stronger than the 22XX. To increase FPS with Discovery the lighter 22XX spring can be used.

 Crosman originally used the same stronger spring in Discovery and older 17XX & 22XX CO2 models. I recommend using the newer 22XX spring as a replacement. It fits all variants of 1740, 2240, 2250, 1760, 2260, 2300T, 2300S, 2300KT and 2400KT.

 As you can see in the second photo the springs are different lengths. Both sizes fit the same valves. The shorter spring doesn't compress very much so it has to be shorter to fit in the valve. The longer one easily compresses to fit with the correct tension.