I’ve had pretty decent results with citric acid and hot water. Preceded by agitating in hot water and dawn. Follow by tumbling in walnut hull media with some New Finish added. Cases come pretty dern clean.
^^^ This.
There was a detailed discussion on another forum about wet cleaning brass
without stainless pins, it works quite well and greatly simplifies the process. Some use the Frankfort Arsenal wet tumbler, some use the Harbor Freight rock tumbler, I got the dual drum model to try. Im impressed. I cleaned some brass that had been in a basement flood then left in a wet plastic bag a couple years before i discovered it. It had some nasty corroded spots which mostly cleaned up well, much better than the dry tumbler ever did on similar things. I think they would clean up even better with a little more time, but I was surprised how they looked after the first attempt.
The common method has been to first wash muddy or really dirty brass in some water with a bit of dish soap, then run it with Lemi-shine dishwasher additive, which is citric acid. Its available at walmart and similar places pretty cheap,
https://www.walmart.com/ip/Lemi-Shine-Dish-Detergent-Booster-Gets-Rid-Of-Hard-Water-Spots-12-oz/15724190?wmlspartner=wlpa&selectedSellerId=0&wl13=5403&adid=2222222227715724190_117755028669_12420145346&wmlspartner=wmtlabs&wl0=&wl1=g&wl2=c&wl3=501107745824&wl4=pla-293946777986&wl5=9022197&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=local&wl12=15724190&wl13=5403&veh=sem_LIA&gclid=EAIaIQobChMI1-Ov2p-G-AIVGJfICh2RCwIuEAQYASABEgK8TfD_BwE&gclsrc=aw.ds It doesnt take much, like a 1/2 teaspoon or less in the harbor freight tumbler, too much will turn the brass pinkish colored. Some followed with the Armor-all wash and wax stuff which is supposed to help run through the size dies slicker, but I havent tried it so far. Anyway, one guy was processing 5 gallon buckets of brass in a cement mixer to clean it, then drying in a food dehydrator dedicated to brass drying. I just used towels laid out in the counter, others used window screens. If anyone is interested in reading more about it Ill find the link. I dont recall anyone that previously used pins saying theyd use them after trying it without them. Some said they made the brass too clean, as in squeaky in the expander die, but without the brass looked good and no squeaking or binding.
I also cleaned some with just the Lemi-shine in warm water in a bucket ans sloshed it around some now and then over a couple hours before rinsing and laying out to dry. It worked pretty well, just not as well as the wet tumbler with Lemi-shine.
After using the wet method, which initially sounded like a pain in the behind, I doubt Ill ever use my dry tumbler again.
For tossing brass in after shooting with black, I think it will work well, and youre most of the way to having it pretty clean. Probably shouldnt leave it overnight without rinsing though.