Recoil Calibration Packs are offered to allow the shooter a choice of recoil springs to calibrate the recoil function when the correct spring rating is not known. The shooter starts with the strongest spring and works down until the desired recoil function is obtained. Each Pack contains one each 11, 12, and 13 lb recoil spring do dial in your pistol's performance. Three extra power firing pin/striker springs are also included.