On balance I used to leave the bores of weapons dry. Not oiled. That way it is easier to pick them up and look down their barrels for rust or any other nastiness. And as unoiled it is easier to do that you are more likely then to actually do it. Rust can form in what appears to be sn oiled bore and yet the oil can 'mask' it. If rust forms in an unoiled bore it gets seen. But never, never, never shoot any weapon with oil still in the bore believing that the first shot will 'burn it out'. For that first shot down that bore...if it is oiled...will give increased pressure, increased thrust on the bolt lugs if the chamber also remains oiled, and in BOTH rifled and smothbore barrels the risk of a ring bulge. It's bad practice. Always with a weapon firing a cartridge clean your bore (and chamber) before firing even if afterwards you don't save of course if it's a .22 Rimfire. And I always store shotguns barrel down if I do ever oil them. For mineral oil can run back, pass through the striker holes in the breech, and rit the head of the stock unseen.