For awhile now I've thought about making my own custom gun because I hear a lot of people giving KWA flak. I want to have something reliable to back me up (or even replace) my KWA when the time comes. I'm planning on using a JG M4 S-System as a base gun. All I need to know is what kind of parts to look for. I'm on a $300 budget as far as internal parts go.