Prometheus Non-Linear Irregular Pitch Airsoft AEG Upgrade Spring
(Power: M170)

"Bought the MS 70-85 for a CYMA AK-47 60th anniversary edition rifle. We play mostly CQB got the gun from a mystery box where excited to use it. But our field is limited to 350fps. We bought a M-85 hoping to take it down below 350fps. This kept the gun shooting about 370fps+. So we bought this hoping to get it below 350 without modifying anything inside the gear box besides the spring. This indeed did take us all the way down to 320 FPS. If you are looking for a spring to decrease your FPS below 350 and are using a longer gun try using this spring.

"A lot of people say a spring is a spring but when it comes to this one. The Prometheus spring has been the most reliable spring that I have ever used. I used it in all my airsoft guns. I highly recommend getting this you won’t be disappointed

"Could I put this in my Matrix M4?