I dumped maybe 500 45 ACP brass into the kitchen sink filled with hot water and white vinegar. Soaked for a half-hour or so and sloshed them around a bit. Then rinse. Spread them out on a towel to dry overnight.
Wow, they really cleaned up good. Anyone else ever try that?
It's been a common practice for many years. Old hands know it, many of us who only started reloading post "tumblers", just don't know about it.
Vinegar soaking is perhaps the only practical way to remove the deep tarnish stains from blackened brass. That, followed by normal tumbling, will restore just about anything to factory-new lookng brass.