I tumble in a separate batch of corn cob after using Imperial, takes it off in 15 minutes. I use a separate batch of cob so it doesn't contaminate my 'polishing' media.
I think I'm an oddball, but I load IMR 4895 and 69gr Sierra match kings in Lake city brass through a Dillon 550. The gods must be smiling on me, because it throws powder with no discernible difference in charge weights.
Here's the link to the CMP site for corrosive primed GI 30 06. They're all somewhat collectible, so worth a little research.
Noncorrosive Chart - CMP Forums
I tried to post this earlier, but it got flagged for moderator approval. Numrich Arms/ Gun Parts Corp is a parts house in NY, shows the sight available for about 22.00