You will most likely have to do edits to the flakspec file as well.
files/gamecore/flak
Just compare the stock gg grenades with the fpsc flak files from EAI's pack. See what needs to be adjusted. Same with the gunspecs.
If you want the weapons to work properly in GG with shader effects and a more modern appearance, you can follow this tutorial
here. But that just on the side.
-Wolf
