The pink on yours may be deeper zinc loss, then. Basically, the polish took all my pink off, which is how I know it wasn't deep (polish doesn't remove much metal). This was corncob with Lyman's green polish added and run in an old Lyman Turbo-tumbler. I'm also wondering if it's possible for the stainless pins to burnish the pink copper up against the surface rather than removing it. I wouldn't expect so, given how well it takes carbon off, but then the carbon is more brittle.
Somewhere I have an old .45 Auto case I found at the range that was heavily corroded and that I put through this process. I can't recall if much pink was left after polishing or not. I'll keep an eye peeled for it and post a photo if it turns up.
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