I wasn't aware there was more than one kit for the PSG-1.
All of the PSG-1 kits I've installed have been Systema FTK12, which contains the 300% spring.
Correct me if I'm misinformed with an official link.
Official reference:
http://www.systema-engineering.com/E...eproducts.html
Follow: "FTK > PSG-1"