Among factors leading to damage of the bore of a firearm are direct chemical attack and galvanic action (electrolysis). These can result from deposits of lead, cuprous alloys or chemical salts on the ferrous bore. Fired weapons which have not been cleaned of deposits from the projectile of residue from primer and propellant are subject to continuing damage. Environmental factors which can contribute to damage are discussed, including humidity, temperature and industrial air pollutants such as sulfur dioxide, nitric oxide and chlorides. Cleaning procedures are discussed. -- AATA