Butlerford and others
Cleaning brass is easy too, get some 2mm ceramic beads from BuffArms and drop them in a vibrator bowl. Add your brass, a little water and a little soap and vibrate for an hour or two. Let them dry and then polish if you want pretty brass. No mess, except dumping the brass/beads into a collander, and no brushes!
I haven't been to a Cowboy shoot, so I don't know if you can do this there, but I take a plastic bottle about half full of water and soap to the range with me, and de-cap and drop the cases in this at the range. After driving home they are somewhat agitated. I drain this, add new water and soap, and dump it into the vibrator. BTW, it's an hour+ drive to and from the range, depending on traffic.
My dad taught me to clean everything after I shoot it, so the parameters of the question don't fit me. Let me say that I often shoot black and smokeless in one trip to the range, and it's noticably easier and less messy to clean the black than the smokeless. The only exception to this is when I get some leading, but that's another issue, and common to both.