I see no problems with choke tube guns being stored muzzle down.
On why I agree on storing muzzle down, it is not a question of a large excess flowing down the barrels and into the head. A small amount over times moves down regardless. No different than solid glass panes that gradually over time get thinner at the top and thicker at the bottom with time. italiansxs you are right that the threat may not be as great if you do not over oil, but I believe even small amounts of oil will move over time.
I look at it in terms of muzzle down is not a problem, and no risk. Butt down is small risk. Why risk at all?
I store all my good guns muzzle down and only my black guns butt down.
