Thanks HS, Walt and Destructo. I called today to CZ-USA, and their gunsmith Mike confirmed what Walt said: the factory spring is a bit weak!! He said I should go to a 15-16 pounds aftermarket spring. According to Wolff, the factory spring is 14 pounds. Since I live in South America it is easier for me to order both (slide stop and spring)from a company with a web site like Denny's Shooters Supply, but they only stock EAA parts (not CZ), are they good quality and fully interchageable? Thanks again.