Yes, all G4's have the standard Combat Machine GB...
Good for a project, but not good out of the box. The FMG4 series is the only G4 that is not a G&G gun. It is made by VFC and is much better internally.
Marshall JCM-2000 + Marshall JCM Cab
JG M733 Enhanced
VFC M4 (not sure which one it started out as)