I've been playing around with the power piston spring kit that Cliff offers online, and was curious how they compare to some stock springs. So, I simply stacked 25-cent coins on top of a PP with each spring installed, until the little stainless APT peg was held steadily below the top of the PP bore.
I don't consider the results to be very quantitative, but I can pretty definitively rank the springs:
STRONGEST
17085213
Black
Green
Blue
17085226
17084226
Orange
WEAKEST
