Ok I've just about finished a full internal upgrade on my M16A3 (tbb, helicals, hi torque motor, quick change spring etc) with the idea of using as a DMR. Currently running sub 350fps just to get used to using it semi auto, but with ability to switch to full if it gets too annoying lol!   Anyway question I have is if I go the whole hog to 400+fps how do people lock their gearboxes to semi only? Just via a mosfet, or by some physical means?   Cheers.