Finally found something that does the trick. Not sure if it's safe on firearms themselves; you should really just use Powder Blast Break Free or something similar to clean them. But if you have a countertop or whatever that's become gray with powder residue, a product I found at Wal-Mart called "Restore4" does the trick. It's a solution of 7.1% phosphoric acid.
Bring back Reed V. "Pie" TurkPalmer Eustachy.