At a recent show I picked up a load of brass cheaply. I'm guessing it had been stored somewhere damp or bagged without thoroughly drying it after some wet cleaning process. It was a bit green.
I gave it a long tumble and even so it was very tarnished and didn't look much at all.
Doing a bit of on line research there were a couple of household item type cleaning solutions. I went with vinegar, lime juice and salt.
Chucked a couple hundred cases in a big mixing bowl, stirred for 15 minutes, allowed to soak and stirred for another 5.
Fluid at the bottom is runs filthy but the cases have come up really well. Dramatically transformed!
Rinse off in a pasta sieve with boiling water and allow to dry on a towel.