Yeah, I could make the barrel round easily, but I believe that the barrel in Halo 2 is squared off. The round is actually easier for the cnc because it is mostly a plunge and move with a ball nose bit, where the octagon it has to plunge and move a lot to make those angle surfaces really flat and crisp edged.

If I don't get a chance to cut this before I go to the desert, I will definitely do it when I get back in August.