Man... If I only had 100 pieces of 308 brass to tumble, or less, I'd pull out my drill chuck up a bit from my reloading kit, insert a nylon 45 brush, grab a piece of super fine steel wool and hit it.
Fast... Cheap... Easy... And does a good job
Heck... I just made a video so you could see what I'm talking about.
[ame=http://www.youtube.com/watch?v=BYksp1U3guQ]Accurate Reloading 101 - #3 - Cleaning Brass Fast Cheap & Easy - YouTube[/ame]