I don't think you can expect much if any bore erosion from powder in the steel barrels that you find these days, and have been standard for more than 60 years. The metallurgy is very good post WWII. You won't find iron barrels until you go back before WWI( 1917) , and then for most guns, you will have to go back before 1880 to find iron being used to make many barrels. Iron is much softer than steel, and there, you might see erosion.
As Mad Monk. you should be much more concerned with rust, due to failure to clean the gun properly after shooting. The residue contains both carbon, and Sulfates. There are also potassium compounds, and Nitrogen is always present. Sulfuric Acid can be formed with the pressense of moisture in the barrel at any time that sulfur is present. Nitric acid can also be formed. These and other acids can eat stell and erode the chamber.
All acids can be neutrlaized by flushing the barrel with plain water. Thow in a little soap, and the crud will come out in the wash. But, you cannot skip a good cleaning of the gun if you want the gun to maintain good accuracy. Our problem today is that way too many shooters don't want to take the time to clean everything, even smokeless powder guns. These guys are who keep gunsmiths in business. More than one smith has told me that at least half his business consists mostly of just cleaning dirty guns to make them work right. There really is nothing else wrong with the guns.
When I was an asistant public defender, many years ago, a friend from one of the police departments told me the average working life of a gun that is stolen is only about 30 days. That is because the bad guys don't know anything about gun maintenance, or storage, and they often hide the guns in burlap sacks which they bury. Within 30 days, a brand new gun will have no finish, and cannot be opened or fired in those conditions. He recovered a Browning Superposed O?U shotgun taken in a burglary 30 days after the crime. It had been buried in the RR embankment across from the city Train Station in a gunny sack. It had no finish, and he could not even open the action, much less get the trigger to fire. He cried. It was an expensive shotgun most of us have only drooled over in gun store display cases.