Sorry I think you guys misunderstood me , I knew wich spring to change (the main one) and I have watched videos to how to change it , my concern was to change to a what M100? M110? i guess not M110 since in this video
King Arms Gearbox - YouTube it says its M110 and the website where I am going to buy says the FPS is 420 ish to 440 ish. Sorry if I formulate badly my questions , English is not my primary language.