If you want the brass to look like new you'll have to get a wet tumbler with s/s pins. But for a media tumbler using walnut and corn cob just add some polish to it, I use NuFinish, just make sure what ever you use doesn't have ammonia in it..
Stainless steel OR put a glob of Brasso in your walnut/corn media - it will make give them a real nice shine that lasts a real long time
Brasso is not particularly good for cartridge brass. I believe it contains ammonia which will affect ductility.
I hate to be a naysayer here but stainless pin tumbling will NOT give you the brightest possible brass (I have one so I'm not just blowing smoke). The brass WILL be extremely clean inside and out but the stainless pins (especially new ones) create thousands of tiny microscratches on the brass which prevents a truly blazing shine.
While compounds like Nu-Finish will give you more of a shine than SS tumbling the best results I have obtained (and I've tried most of them) is a two step process. First I do an initial tumble clean for an hour or two with Lyman green treated corncob to remove most of the powder residue, etc. Then I tumble again for another two hours with a mixture of a dash of jeweller's rouge (jewelry polish) and paint thinner (about a teaspoon) in finely ground corn cob media. The cases come out not just clean but almost mirror reflective. My brass cases are so shiny that they are hard to distinguish from nickel cases.
A lot of people will say it`s not worth the effort and they may well be right. However, I figure if I can`t be the best shot (and I seldom am) I`m at least going to have the prettiest reloads on the line (and I usually do). And nice, shiny smooth cases can only improve cartridge feeding.
as per OP, this is for his girlfriend....



























