I've long since moved on from tumblers to ultrasonic cleaners and dumped expensive cleaners in favour of cheap 'own brand' cola. Now the wife commented that some old biddy on a TV show had used the same cheap cola to clean her toilet and i wondered how effective the cola alone would be cleaning cases ; no ultrasonic cleaner, cloth, wiping or agitation in any way.
I dumped 50 old dirty 7.5x55 cases in a half empty 2 litre bottle of ASDA cola and left them for 24hrs. You'll have to forgive the quality of the pics, but the results are great. A quick sloosh round under the tap and left to dry afterwards and the results are pretty much as good as a couple of long cycles on the ultrasonic cleaner.
19p for effortless clean brass without any tumblers, ultrasonic cleaners or fuss. I can live with that.
Comparing one before and after: