We've been told that a Shroud is able to disperse the energy blasts fired by ethereal canons, but I wonder how well they would put up against traditional (i.e. metal cannonball) weapons. After all, we know that ether-silk passes through the shroud without problem, and the fact the you can feel wind when diving means that air can pass through as well.
P.S. In our world, bronze cannons were still in use into the 19th century (it was more "springy" than cast iron), so iron rot isn't really an argument.