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.