A lot of CQB sites run a 328 fps limit rule so I would get your gun downgraded anyway if you want to play CQB. Its a simple spring change most guns have an online tutorial somewhere on how to do it.You need to know what spring is inside and what it actually chronographed to know what spring to get, or you can just take it into a shop and get the shop to do it if you dont feel like taking it apart yourself. Im sure a few forum members own RM4's and could guide you through it as well.