For the insides, I use a bottle brush on an electric drill like someone mentioned. You can add steel wool and tumbling media with the bottle brush to get a bit more 'shine', as well as chemical polishes. The thing to ensure with steel wool is to thoroughly clean any remnants out--it can cause rust and scratch the barrel. Another way to speed the cleaning process is to wash with hot soapy water--rinse with hot water--dry in the oven--then tumble. Cleaning the insides can be time consuming if using the bottle brush method, so I only use it for select hunting ammo.