If "lots of oil" is going to be used during storage, it is a good idea to store the gun, "muzzle down" to prevent an accumulation of oil at the breech.
This is especially important if the gun uses a "patent" or "chambered" breech which has a small flame channel (hole) connecting the bore with the vent hole.
Many of the currently made guns use this type of breech.
If "lots of oil" is used in the gun and the gun is stored muzzle up, that oil will accumulate in the flame channel. This usually contaminates the new powder charge and forms a dam, blocking off the flame channel. If the flame channel becomes blocked off, the fresh powder can't make it all the way to the vent hole so in effect, there will be no new powder at the vent hole for the flash from the pan to ignite. I might also add, even if some powder does make it thru the flame channel, if it is fouled with oil, it won't ignite easily which will lead to "a flash in the pan" and no ignition.