Blitz - good point but I think that problem is the exception rather than the rule.
All of my barrels are stainless steel and I have never experienced and rust what-so-ever. But others have claimed that moly could cause rust in non-ss barrels.
In a regular steel barrel it would have been a good idea to run an oiled patch through the barrel after shooting, as a precaution. I usually clean my barrels after each session and leave a film of Shooters Choice or similar p-roduct in the bore until the next outting. Guns left for any period of time routinely get treated with Break-Free CLP.