For Best Performance With Hot Loads
Extra power outputs for optimum functioning with hardball and hot
handloads. Each spring comes with an extra power firing pin
retraction spring to offset the increased slide thrust.
Big Book Catalog, Issue:66, Page:217
New Product Supplement, Issue:502, Page:000
Personal Protection, Issue:01, Page:018
SPECS: 1935, 9mm's original spring averages 17 lb.