I have always seen the recommendation that you should run a light coat of oil inside the barrel to protect against rust. I believe this was more of a way of protecting against rust for long term storage though, as I have also seen it mentioned that you should remove it before firing. Which begs the question of what to do for your carry pistols? They are both subject to rust during storage (carried in holster) and subject to firing at a moments notice. Is it a good idea to risk having a fouled primer in the chamber by putting some oil/grease down the bore? Is it even needed with pistols such as H&K/Beretta/SIG which have excellent surface treatments of the barrel to protect against corrosion?