KWA gears, bearings, cylinders, air nozzles and cylinder heads are all proprietary, some consider the bucking or hopup (still a 2-piece though) to be as well. I have seen a KWA's 2GX gear shear its axial under normal load. Not sure how that happened. I've also seen them tear their pistons pickup tooth clean off. I like them for the most part but as an owner, which I'm not, it would be very important to me to know these things prior to purchase. Proprietary gears is kinda a big deal to me. I also like the 2GX bucking but they don't last long enough, IMO. I would consider their motors on par with the G&P M120 which is a fantastic motor. KWA's are some of the best sounding replicas out of box let alone on the field.