With the general use of plastic shells many yars ago many began experiencing chamber rusting. Some component of the plastic was often blamed. The truth turned out that was not the case. Upon firing paper shells a left a waxy deposit in the chamber which helped to protect them fron rust. Plastic shells had no such coating so the chambers were left dry. Often time the brushes, mops etc used for cleaning the bore were not large enough to clean the chamber. As the chamber itself appeared clean many simply neglected to follow up on the chamber. In many climate conditions this left the chamber susceptable to rusting. As far as I know though there is no difference here whether the gun is steel or damascus.
