First Factory - PSS2 170 Spring for APS2

This spring have 9mm inner diameter. I use in a Classic Army M24 with Advanced Cylinder Kit, the spring is actualy very similar in FPS compared with the default spring that comes in the CA kit. This spring will provide almost 470fps in a CA M24. It´s expensive for a spring but it is a very sturdy product, will be hard to loose FPS with this spring even if they are used for a long time.