Aqua blasting is all the rage at the moment. I’ve been doing it for years at home using a cheap B&Q pressure washer (£25) and a sandblaster pick up lance (eBay £9.99).
I used to use special sand that you had to buy from B&Q, but you can use dry sand from a builder’s merchant or glass beads if you want to be posh. After you have done your cases this way all you have to do is clear lacquer them and they look just like the original, not polished. There seems to be an obsession with polishing casings but this gives good results.