5% citric acid solution (add 7 ounces to a gallon of water) is an old arsenal formula from before neck annealing (1920's). It leaves the surface much less activated than even vinegar does. I've had vinegar cleaned case turn purples and greens if left exposed to air long enough without polishing, which colors tended to camouflage case whereabout when policing brass in grass. Citric acid cleaning rapidly removes oxides but leaves the metal fairly yellow and doesn't etch it very much. 5%-10% solutions are used in conservation of recovered heavier brass objects from shipwrecks for this reason. It stays yellow, though the yellow does darken some over time.
You can use a lot less citric acid if you intend to dispose of and not reuse the solution. You can buy ten pounds for $27, postpaid, from
this outfit. I usually add a squirt of dishwashing liquid to the citric acid solution to help suspend dirt and dissolve oils.