when i next rebuild my mp5k (the gear box is going to explode at some point), i am going lonex gearbox shell, motor, and bearings, with shs gears. i have had bad experiences with guarder 6mm bearings, and G&P motor's
I know that 0 out of the 12 sites that I play at would allow a 500fps AEG. 450 to 425 is the regular for a DMR. 500 for a bolt action sniper. As for the rest of your question I cant help. I'm simply pointing out that you probably don't need to do it.