In reading your past posts, I'm quite sure you have flushed out all remaining grit from the polishing process, from all parts including the decap portion. This was my first thought and I figured I'd pass it on.

I had an old used set of RCBS dies for 44 WCF that did the same, polished it out, some scratching still remains, but in shooting black powder it doesn't seem to matter much.

Maybe I'll revisit the issue.

THANKS
DOWNWIND

PS Are you starting with CLEAN cases?

If so, maybe some grit being transfered while loading?