By casting, I meant the plastic/aluminum cast of the gun itself. The dummy gun. "Gun Mold" isn't the right term since the "negative mold" is what the plastic is poured into to make the dummy (positive cast) gun. I realize the the gun mold term is used all the time though.
I've done plenty of metal casting in the past so I can't quite bring myself to call it that even if it makes more sense to other people.