When you use the word " Pitting " I tend to think of potholes in the street that will break an axle, or tailpipe if you aren't careful. Shallow pitting can be taken out with lapping compounds, even toothpaste, or JB Bore Cleaner. The Green Scrubber can also be used. Steel wool will knock off surface rust, but generally is too soft to do much about pits.
There is a technique referred to as "fire-lapping ", where you coat the patch you use around a round ball with lapping compound, and fire the gun off, repeating this process, until you have removed the rust or shallow pits.
For deep pits, there is nothing that can be done save re-boring the barrel to a larger caliber, if that is even possible. Sometimes its cheaper to get a new barrel! I would not go to that expense unless the exising barrel absolutely will not shoot at all.
I have an old German Mauser I bought from a large discount store. They had shot corrosive primers in the gun, and it had not been cleaned. Both the lands and grooves were pitted. I jsue JB BC on it repeatedly and finally got the lands shiny and polished. But the grooves remind me of pictures of the Burhma Road! The barrel still shoots metal jacketed ammo okay, so unless I decide to change barrels to a new caliber, I will probably keep this as is.