Originally Posted by Doombringer
What Mist3r.B means is that if you mix different brands of gears, piston, etc... inside your gearbox, they might not fit. The tolerance in the machining process is not exactly the same from brand to brand so they might not be an exact fit. To minimize those chance of problems, you should stick to the same brand for all your gearbox parts.
Exactly, for exemple a G&G V2 gearbox will not fit properly in a G&P m4 body . It also apply on external parts. Those cost a lot and can be hard to adjust when their a fittement issue. I know pleople who spent 5h making a KA RIS fit a G&P receiver.