This is a copy / paste off another forum.
Periodically, some new shooter comes on the forum claiming that he needs to "SEASON" his barrel.
Today's modern barrels are made of STEEL, an alloy of iron and other metals, which produces a much harder metal. Muzzleloading barrels are made either of a soft alloy with lead in it to make it easy on the cutters (12L14), or harder steels, like 440 alloy steel, which withstands high pressures, but is harder on tool bits. They are not made of the iron that was used in the 18th century.
We don't season Steel, because its next to impossible to do (those pores in steel are filled with trace elements, so there is no room to allow oils or other substances to be burned into the pores), and its Not necessary for good accuracy, or to prevent rust. Simply running an oiled, or greased cleaning patch down the barrel AFTER seating a PRB on the powder charge, will protect the front portion of the bore from rusting.
Today, the most common IRON product to be found in a home is the Frying pan, or "Skillet" used to cook. Even those are becoming more rare- often only seen in camping equipment, rather than used in the home kitchen. Skillets are made of CAST IRON, which, unlike Wrought iron, have large PORES in the surface.
We SEASON cast iron skillets (but not steel, aluminum, or Teflon coated skillets) to fill the pores of the steel to prevent rusting (RUST adds a terrible taste to food), and to make a very smooth slick surface to use to cook certain foods, like Eggs.
To Season a Frying pan, or skillet, you first rub the surfaces of the skillet with shortening, or lard, or fat. Coat it liberally, so that you don't miss a spot. The place the greased skillet in an oven heated to 500 degrees!
Leave the skillet in the oven at that high temperature for at least an hour. Then turn off the oven. When the oven and the skillet cool to room temperature, inspect the skillet. If there are spots of plain steel showing, or if the entire surface of the skillet is Not Black and Smooth, and slick to the touch, repeat the process, until it becomes that smooth, black Greasy feeling surface (a dry grease- not gooey). With a properly seasoned frying pan/skillet, you can fry eggs on them, and the eggs won't stick to the pan.
In the 18th century, when barrels were forged from soft iron, the barrels were seasoned, often by the gunmaker. He would coat the rifling with a thick layer of fat, then heat the barrel up in his forge, and burn out the fat. What was left in the open pores of the iron bore was the "Seasoning", that prevented rusting inside the barrel.
I am sure that somewhere, in this country, someone is forging IRON barrels. The Possibility exists then, that a shooter could run into a modern made gun, made with a true Iron barrel. I can't imagine the cost of such a gun, considering the labor involved in making such a barrel using the old forging methods, and I would not fire such a gun, since there are cheaper, safer barreled guns available for shooting and hunting.
With Steel Barrels, any attempt at "seasoning" the barrel will only result in frustration, and in a clogged bore, that eventually looks like a smoothbore. The Grooves of the rifling fill up with charred residue, to the point that there appear to be NO more grooves.
This very thing has been observed these past 30 years, in Thompson/Center rifles, because that company's early loading manual spoke about just adding more "Wonderlube" to the barrel if a ball or bullet began to stick in the barrel because the barrel was not cleaned, or swabbed between shots. A lot of people, including members of this forum have made (and probably will continue to make) a lot of money buying up OLD T/C rifles, with the barrels "Shot out", for bottom prices. (The current T/C manual no longer carries that advice, I am told).
The gun barrels are taken out of the stocks, given a good soak for several days with soap and water, then scrubbed well with a bore brush to remove all the crud accumulated in the grooves of those barrels. It comes out in CHUNKS! Typically, when the barrels are CLEANED, they look as good as new, and shoot PRBs just fine. The guns are then sold for a nice profit.
[Plunge a piece of soft wire coat hanger, heated red hot, into a container of oil - any oil. The wire will come out with a smooth, Shiny Black coat on the surface, that is quite durable. It's the closest you can come with modern metals to see what a seasoned barrel WOULD look like].
Years ago, now, I offered to try to help a small local gunsmith, who had just opened up a New shop, get more business into his store, by getting the members of my local gun club to come out, on an Advertised Saturday, to offer to inspect and CLEAN and oil the guns of hunters intending to hunt in the up-coming seasons, for a nominal charge. He looked at me IN HORROR! He told me that if people actually cleaned, inspected, and oiled their guns, he would be OUT of BUSINESS!
He told me that a substantial part of his pre-hunting season business profit came from customers who brought their guns to him to be cleaned and oiled for the next season, having done nothing to them since the last one!
I was raised by a father who Insisted that our guns be cleaned as soon as we got home, and before we did anything else. He inspected our work, initially, and was as hard as any drill sergeant ever heard in Boot Camp.
I can't even imagine taking a dirty gun to a gunsmith, unless it was jammed, and I could not get the gun apart to clean it first. (That's not going to happen with any MLer I have). I would be embarrassed to take a dirty gun to my gunsmith. I obviously was raised in a different world.
If I had to give a truly SHORT answer to WHY we don't Season MLing barrels, It would be, that "we clean our steel barrels, so seasoning is never necessary (nor possible)". Cleanliness is next to Godliness, so goes the old Proverb. The context was different, but the wisdom is still sound.