Basically, shells/bullets fired by movecraft vehicular cannons deposit "spent casings" inside whatever container block is holding the ammunition should it have open slots. These casings can then be dumped into a smeltery and melted down into brass, tin, lead, steel, iron, or whatever other ingots were used in the casings with a chance of 1-3 of any of those types of ingots being returned to you. I'm not sure if shell-specific casings would be added (like fighter autocannon bullet casings or 9-inch shell casings) or if it would simply be like bullet and shell casings or just shell casings. I think this would be a neat logistical feature added that would allow militaries that fire many shells to recycle some of the materials left over kind of like what some do in real life.