Someone told me how they cleaned the oldest and dirtiest range pickup brass using Lemi Shine dishwasher detergent.
Not being sure which Lemi Shine to buy at Walmart and how to use it, I did a search of the THR website and the results show many posts about it.
After the black brass that he cleaned with it, I would be surprised if it couldn't clean up the worst stained brass.
Check out some of the threads about which to buy & how to use it.
He was only using shell media along with it, and only the worst of them needed 2 passes in the tumbler.
Lemi Shine search results:--->>>
https://www.thehighroad.org/index.php?search/34529103/&q=lemi+shine&o=relevance
IIRC he bought it at Walmart for $5 - $7:--->>>
https://www.walmart.com/search/?query=lemi shine&cat_id=0&typeahead=lem
I'm pretty sure that this is it in a 2 pack:--->>>
https://www.walmart.com/ip/2-pack-L...-Powder-12oz-Natural-Citric-Extract/863054852
Or buy citric acid in the canning aisle at Walmart:--->>>
https://www.walmart.com/ip/7-5-Ounce-Citric-Acid/20469602
Read the 1st thread of the search results, it mentions to mix 1 teaspoon per gallon of water, and read more threads for more info:--->>>
https://www.thehighroad.org/index.php?threads/lemi-shine.835991/