I bought this spring thinking it was going to give my Kronos a good 20 FPS boost without making the prime weight overly difficult. In short, I was wrong. The Kronos will definitely hit 120 FPS with this spring but the prime weight is so heavy that I really had to struggle to even prime it once, and I'm a full grown man. Unless you're a weight lifter with biceps of steel I'd recommend sticking with the stock 100 fps Kronos spring.