I have "tumbled" loaded rounds for years, correction hours, but have been doing it for years. I only use clean dry corncob media with no additives.
When TUMBLING as in any type of rolling barrel, fill barrel to top with media so loaded cases SLIDE thru the media and do not tumble in manner that the point of a bullet may contact a primer with sufficient force to set it off.
When VIBRATING, fill barrel with media to minimize cases bumping into each other and to slow the cycling process.
I tumble all loaded rounds, except my 50BMG target rounds due to size, to remove any lubes and fingerprints prior to final cleaning in bath towel and packaging. Handling after cleaning involves using cotton gloves. I have loaded ammo from 1982 that still looks better than any newly purchased ammo, and still shoots better. I seal in plastic bags and place in good ammo cans.
Brass and copper will tarnish slightly due to age and exposed lead will oxidize. Sealing in plastic and again in ammo cans will minimize this aging process.
Your methods and results may vary - your choice.
OldmanFCSA = "Oldman" at www.fcsa.org
FCSA Member, SCSA Member, NRA Member, & AMA Member
"Oldage & Treachery will overcome Youth & Skill"