It appears that I'm not the only one that washes brass before tumbling it.
I'm a retired Clinical Engineer and I've maintained several industrial sized Ultrasonic Cleaners used to clean surgical instruments over the years as well as smaller ones. They work by small bubbles (microscopic) forming and bursting on the liquid/solid interface. Tap water doesn't work too well because it contains dissolved minerals and the inherent surface tension is high, so it doesn't flow freely into the smaller nooks and crannies. Distilled water with a couple drops of detergent per quart works pretty well for most applications, but adding vinegar and salt helps remove tarnish from brass. There are specially formulated solutions for cleaning specific materials, so check the application notes when buying premixed solutions.
I have a circa 1975 L&R unit with a half gallon tank that's cleaned a bunch of things including gun parts and
badly tarnished range brass. I used to run all of my fired brass through it, but these days I just toss them in a gallon jug and shake them in a solution of distilled water, vinegar, salt and D-Lead detergent, let sit for a while, shake them again and then rinse/dry. Of course, my goal isn't to get them squeaky clean. All I want to do is remove the GSR and keep the airborne lead residue to a minimum while tumbling.
I use a vibratory type tumbler with walnut media and a little NuFinish so they shine (SWMBO likes pretty ammo) and slide into the resizing/decapping die easier on my turret press.
Some reloaders don't clean their brass at all, most tumble it only, while others wash it only and a few of us do both.
Dirty, clean or shiny, it all shoots just fine, but some reloaded ammo looks better than others.
