Tempered spring with blackening. This spring will provide approx 490-510 fps.
The FPS you get will differ depending on your setup and how good the rifles air seal is.
Spring is 9mm so will fit all upgraded pistons from manufactures such as PDI, Laylax or our own pistons here on this web site. (It will NOT fit the stock plastic piston). For stock pistons pleas use the M150 VSR spring.
When upgrading your rifle we always recommend having a read through our guide: http://www.airsoftsniperparts.com/upgrad ing-an-l96