Why case cleaning is NOT a significant step in any loading manual
Shiny brass does not make a more accurate round. It does seem to give some more confidence and they "say" that is makes sizing easier.
I consider that 30 minutes in 20/40 corn is more than enough cleaning for any case, unless you are digging them up or getting them out of the mud.
I have seen some cases from benchrest shooters that have been fired so many times with light loads that they can actually scrape out chunks of powder ash. However, they didn't complain about the accuracy.