Best bet is to pay a gun doctor to do it if you don't have a quick spring change gearbox. It's not necessarily hard and you could always try before you go to a gun doc but I personnally find that the 20-30$ it might cost you to have it done is better than an hour of internet searching and whinning about things not working out for you. Not to mention that you need a chrony to measure the final resulting FPS after the operation.
Black Coqs - Fireteam Echo
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