The CZ Custom Shop Mainspring Calibration Kit contains main / hammer springs from 10lbs to 16lbs these springs can be used adjust the double-action trigger weight. Testing has shown the 13lb mainspring in combination with a CZC extended firing pin and CZC 2075 Rami firing pin spring will ignite the primers in the factory ammunition that CZ Custom uses. Given variables in ammunition, primers, reloading techniques your results may vary. CZ Custom is not responsible for your results. Kit Contains10LB11LB12LB13LB14LB15LB16LB Note: If the pistol is to be used in critical situations such as law enforcement or self-defense. Reduction of the hammer spring strength may compromise reliability of the firearm.