Wilson Combat’s 17# flat-wire Recoil Spring 5″ .45 ACP chrome silicon 17 Lb. Recommended use- full-Size 5″ .45 ACP shooting 230 gr. hardball equivalent or standard pressure JHP self-defense ammunition with a power factor of 175 000 to 195 000 (Velocity x Bullet Weight = Power Factor). Our testing has indicated that these springs have a service life up to ten times greater than conventional coil springs. Features improves cycling and overall operation .250″ Rod Diameter; compatible with standard recoil spring plug and with Shok-Buff Recoil Buffers.