A&K M249 spring replacement
I just purchased an A&K M249, but it's been upgraded to shoot 400 FPS. I need it to fire at 350 FPS, and the guy I bought it off of said all I need to do is replace the spring with a weaker one. However, I'm new to airsoft, and don't have a clue on what spring to buy or how to install it. I can search YouTube to find out how to do it, but would appreciate advice on what spring to buy. Thanks.