To add to what dpvu said - the JG's internals are fine. Mine has seen several thousand rounds so far. I've upgraded to metal bushings and reshimmed it, but all the other internals are stock. The parts are fine and I don't see the need to replace any internals unless something actually breaks. I would also recommend a spring downgrade, as it does shoot hot out of the box. Mine still has the stock spring. It was shooting 390, but once I added a new hopup rubber, that shot it up to about 425 fps, so I can't game it until I get a new spring for it.