I have a quick question: I have a nuprol rifle, but my gearbox has to change. Promise that the old gearbox is v2, my friend gave me the G&G V2 change. The question is: is it compatible?
are you asking if a g&g gearbox will fit into a nuprol reciever?
assuming your rifle is an m4 variant then yes it takes a v2 gearbox, wether the g&g will fit is a question of maybe.
in airsoft the best you can hope for is "compatible ish" and you may find that it won't quite fit right needing a little adjustment to work.
this is of course assuming there aren't any particular foibles of the models of gun/gearbox involved (eg bolt releases mounted either to the reciever or the gearbox)