Damage Industries is now offering three versions of recoil buffer springs for the AR-15: the standard stainless steel mil-spec spring, the ‘music wire’ spring, a higher-performance spring which eliminates acoustic “twang”, and the enhanced spring, constructed from certified USA-made chrome silicon spring wire, it provides consistent spring pressure for an estimate 750,000+ cycles.
http://damageusa.com/product/ar15m16-spring-recoil-buffer-carbine – Standard
http://damageusa.com/product/ar15m16-spring-recoil-buffer-action-music-wire – Music Wire
http://damageusa.com/product/enhanced-spring-recoil-buffer-action – Enhanced