Many firearms, primarily in the Eastern Bloc, are issued with steel-cased ammunition. Perhaps the most famous example of this is 7.62x39mm, the ammunition used by the AKM and its family.
Steel can be used to make cartridge casings with greater pressure thresholds and at a lower price. However, because it is not as malleable, the chamber sealing is imperfect and more gunk gets thrown at the action. Furthermore, it must be coated with lacquer or polymer to ensure reliable extraction, as steel's texture is rougher. Steel cartridges work better in firearms with strong actions and loose tolerances, such as those produced in the Soviet bloc.