Equal parts Murphy's Soap, rubbing alcohol and hydrogen peroxide works very well on the gun and cleans your hands as well and is very popular with shooters using BP for guns in Cowboy Action Shooting. Give the barrels a couple of squirts, let sit for a few minutes and then push wadded up paper towels down the barrels and repeat as necessary. Usually 2 or 3 passes is enough.

While waiting a couple of hours or a day to clean the guns won't hurt them, I have found that cleaning them right after I am done shooting seems to make the clean up be easier then waiting until the next day.

I have become addicted to English hammered shotguns to the detriment of my wallet.