The origin of the phrase “keep your powder dry” comes from the era of muzzleloading blackpowder weapons, where damp powder was often much more than just an annoyance, it could lead to a painful death at the hands of Indians or large carnivorous mammals.
My co-host Squeaks seems to have encountered the modern day equivalent of keeping your powder dry, which would seem to be the much less elegant phrase “don’t overoil the chambers of your carry gun and then leave ammo in there because the shit will corrode and foul your revolver”. For the record, this is why I recommend the Bore-Snake (hur-hur) to people, especially revolver shooters. I use the Snake not only the barrel, but after I patch the chambers, I’ll run them through with the Snake to get any lingering grit out, plus the Bore-Snake removes any excess oil that I might have left in the gun.
As much as I hate to sound like a product placement guy, if the zombies did rise, I would grab a Bore Snake to go along with my survival guns, because a dirty gun is almost useless to me.