To the O.P.: Lots of ways to do it cheap.....for 35 years I just wiped them off, leaving the tarnish and loaded them.
Then I sprung for a Lyman 2500, cheap 20/40 corncob from Zorro, and a capfull of Dillon polish......bling outside, dark inside.
Then a Thumbers wet tumbler with stainless steel media, lemishine, and Dawn dishwashing liquid.
My how spoiled I've become....
No the wet Thumblers method is not cheap, but it's a one time expense. I don't even remember the hit 3 years ago, but I'll enjoy the reward for many yearsT to come.
Xandi asked, "So will ss pins with water clean both the inside and the out side of a case?" Yessssssir! See below:
I have this funky 7 station press with room for a dedicated powder cop station no matter what I load.....only I've never liked powder cops.....too easy to ignore them unless they beep......and I hate beeping stuff on my tools. So I made a prototype mirror station, and that wouldn't be worth 2 cents if the cases didn't reflect light.
But they do....thanks to stainless steel media wet tumbling. No more squibs or double charges.
The following short, one-handed, & very shaky video of a .308 (7.62 LC) case is a better demonstration of the concept!
No, this is not trick photography, and its not a shallow .45, that's the inside of a .308.
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Click on "vimeo" if you'd like to see it bigger.*****
----------Once there you can even make it full screen if you want.
https://vimeo.com/281564743