Factory weight is 9 lb. Use heavier 11, 12, or 13 lb. spring to improve cycling reliability, especially with hot loads. The LCP recoil “spring” consists of an outer and inner spring; each recoil spring pair comes with an extra-power firing pin spring to further promote reliable ignition. Recoil Calibration Pak contains one each 11, 12, and 13 lb. recoil springs, plus three extra-power firing pin springs.
Big Book Catalog, Issue:66, Page:217
Personal Protection, Issue:01, Page:018