If you've put any decent number of rounds through a reloading press (particularly a progressive), your bins will eventually look like this. This is grime from the cases, old case lube, and various other contaminants. It's resistant to soap and water, but it comes off very easily with the application of Hoppes #9 bore cleaner.
This is the Akro bin into which completed rounds from my Dillon 650 drop.
As always with Gunwiki pictures, if you click the thumbnails, they expand to a larger resolution.
The "before" picture. The deposits have a somewhat gummy texture, and are primarily powder residue, with some embedded brass shavings.
Applying a small amount of Hoppes #9 powder solvent. A paper towel was used to wipe it up.
The "after" picture - all clean.
-- SeanNewton - 08 Apr 2012