Sons of Liberty Gun Works Extra Power Rifle Buffer Spring Black. This spring is wound from 17-7 stainless steel which is then passivated for maximum corrosion resistance. This spring offers roughly 10percent additional power over the standard milspec rifle spring and pairs well with our rifles (having been built to use extra power springs for years) as well as most other suppressed firearms. As this is a rifle length spring it is only for use in Intermediate/A5 length and rifle length buffer systems. Specifications for Sons of Liberty Gun Works Extra Power Rifle Buffer Spring: Manufacturer: Sons of Liberty Gun Works Color: Black Fabric/Material: 17-7 Stainless Steel Features of Sons of Liberty Gun Works Extra Power Rifle Buffer Spring Spring Matte Finish Black 17-7 Passivated Stainless Steel Rifle length for use with A5/Intermediate and Rifle length buffers XP strength is roughly +10percent over traditional rifle length springs Package Contents: Sons of Liberty Gun Works Extra Power Rifle Buffer Spring Spring Matte Finish Black Sons of Liberty Gun Works SOLGW-XP-INT-SPRING: Extra Power Rifle Buffer Spring Black