[Bdot]

i have a m4, and i am wondering what gearbox i should get for it. Its between a M170 systema Magnum gearbox and a systema M120 torque up gearbox. If i was to get a M170 i would put a M120 spring in it so i am able to use it at places. also if i got the M170 and put a M120 spring i would change to a lower battery so it doesnt break. I was wondering if anyone knows if getting a M170 and putting a M120 spring in it or just getting the M120 gearbox which one would work better. because i know the M170 has better parts but would it work better or is it better just to get the one thats made for it. also do u think if i got the M170 itll have a lot of problems? thanks