This is a proprietary spring only for use with Sprinco Recoil Systems shooting 139 or lower Power Factor loads such as 115 gr. target rounds and other lower power factor competition loads.) (FULL DISCLOSURE: The WHITE spring is only ONE pound lighter than the YELLOW spring at full Slide retraction. It is not guaranteed to work in all specimen pistols, as it is right on the razor’s edge of functionality due to the basic functional design recoil spring load demands of the platform. This is neither good nor bad, “It’s just Physics”, dictated by the functional demands of cycle of operations for this great pistol design. The YELLOW spring has a longer historical duty cycle than the WHITE spring, and also has a better closed load spring pressure than the WHITE spring. Purchase this spring only if you are adventurous, as we cannot guarantee functionality in your specimen pistol)