what size wallnut?

[soldier-of-the-apocalypse]

I need to get 100 lbs of walnut shell today what grit do I need to get. Im about a block from united western and they have 12-20 large, 20-40 medium, 35-60 small and I'm also gona get a bag of corncob what size of that should I get?
I tumble all my .223 and pistol calibers in walnut.

[Great-Kazoo]

Fine grit / smaller the better. providing you tumble Then Deprime