I own mostly all side lock shotguns, L.C. Smith's and the only ones stored muzzle down are the ones that I have are near the door opening because of limited floor space in order to close the door.

I know some here do store their shotguns muzzle down, but I take mine all apart when I get them and I have NEVER seen oil built-up that would warrant me to store them muzzle down.
Where is all this oil coming from?

David