Hoang67, CGW says their extended firing pins are "for use with reduced power hammer springs only and selected hammer spring varies with model, please contact CGW for recommendations". I have seen recommendations that you should not use more than a 15# hammer spring with the extended firing pin. I also use the 13# hammer spring and extended firing pin in my P01. I don't bother switching hammer springs when I shoot my Kadet2. I have a very occasional light strike and failure to fire, but have chosen to live with those as I am only using the Kadet2 on the practice range. You may want to swap back to the heavier hammer spring depending on your results with the 13# spring, or if you are planning to shoot competition.