You could try, Lemishine a liquid type polish. Some reloaders use it in the wet tumbling cleaning of the shell casings. Or buy a bag of citric acid and make up a solution and try that as it is also used by some. The citric acid powder is used in brewing, baking and as a supplement.
Lemishine is sold @ Wally World,and other stores.
The swimming pool additive that is used to raise the pH of the water(sodium bisulfate) Is used by metalworkers and jewelers to clean (pickle) copper and brass along with silver before soldering.
It works better if heated, NOT BOILING!
As been said in another post the blanks are made from brass alloys or nickle. The pickle will brighten both, but be aware don't use any steel bowls,can or utensils in the Pickling Solution as the ferrous material will change the solution into a flash plating solution and give the brass a rosy look!
Used a glass jar and then pour the mess into a strainer then rinse.
:clown: