ALL STOP! I don't care WHY you're making this sculpture. I don't know where you live, but if this is for a class at any school that is actually worth its salt (accredited), then odds are that it would be highly illegal to exhibit a sculpture made with real guns or even with non-functional PARTS of real guns on campus.
I see that you're a grad student, so I don't think you're stupid. Even if you are planning to make this sculpture and put it on display somewhere off campus to be viewed by whomever is supposed to be evaluating it, you may be opening yourself up to a negative reaction. It has been my experience that Academia is hostile toward the 2nd Amendment in general. This would matter less if you were an undergrad student, but as a grad student, your relationships with other instructors and administrators matters a little more than it used to, doesn't it?