Armaspec Stealth Recoil Spring, SRS, AR Buffer Replacement Kit, Contains Drop-In Recoil Spring, C, H, and H2 Buffer Weights, Black ARM253-AR15KIT The Stealth Recoil Spring SRS GEN4 is a self-contained multi-stage drop-in replacement for your standard buffer and spring. The SRS is designed to keep the buffer spring from rubbing against the inner wall of the buffer tube providing smooth" quiet operation and the second stage helps reduce the felt recoil significantly.