You're thinking too much in terms of 21st century western throwaway-society. Refilling cardridges is child's play here on this very planet, today. http://www.youtube.com/watch?v=Arjc_tKofhA&feature=related You just need the empty cardridge, fill it with an explosive of some sort (in a pinch smokepowder will do) cast a bullet and attach it to the cardridge... Of course it won't be as efficient as industrial ammo, yes the gun may explode in your hands but it would be fine enough for surviving in the wastelands. Making ammo for gauss-weapons should be even easier, you just need a casting-mold and the right alloy. Caseless ammo and Energy cells would be irreplacable, though.