EDIT: YES I FINALY GOT AUTOCAD!
I haven't installed it yet, but from what I saw of it you export the model as a .obj fileErm...i all suddenly forgot what to do after that...there is a tutorial somewhere on it though.
I think the barrel could be a little smaller in diameter, but looks great
No, don't make the barrel smaller on an energy weapon. You want the barrel to look like it contains a bunch of electromagnetic coils and a cooling system or something. Simple round steel barrels are a mark of conventional rifles.