I just finished building a new brass tumbler for my .223 and 40 cal and bought corncob from a local pet store. Ran about 150 .223 cases through and it didn't do too bad. Not as shiny as I expected, but clean. The big problem I had was the corncob was stuck inside every .223 case and it took me over 3 hours using a spring hook to clean the brass of the corncob. I thought a lot of people use petstore corncob so I tried. The problem is the grains are too big or too small. What do you reloaders use. I might switch to walnut shells thinking that the shell will be smaller and not jam in the cases. The corncob will be perfect for 40 but not .223. Any help will be appreciated.