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 Pak contains several recoil springs and offers a savings over buying them individually. Three extra power firing pin/striker springs are also included. Contains one each of 17.5, 18.5, 20 and 22 lb variable recoil springs and three extra powder firing pin springs.