Shilen laps stainless barrels. I did a plant tour about 15 years ago and they actually apply a thin copper plating to the inside of the stainless barrel to help lubricate the button used for rifling. That copper has to be removed by lapping afterwards. Not sure if they do it it or not on the...
They are the only barrel manufacturer that I am aware of that offers this as an option. I’m assuming most do this without the additional cost. Obviously there are some that don’t do it at all.