Why don't they produce heavy artillery in the Wasteland?
In the three-pronged industrial complex of the Wasteland, they seem to be able to manufacture quite sophisticated technological marvels, such as the complex war rigs. The CGI/matte painting depiction of the oil refinery and bullet farm tell us that they have plentiful energy and ore. So, why not make cannon barrels and artillery rounds? Why make war bois plunge to their death with explosive spearheads?
Maybe that sort of thing could secure the Fury Road connecting the 3 important facilities and fend off the marauders, so that each trip with the rig would not have to be a monster truck demolition derby. Just saying.