From my experience, fire lapping doesn't remove deep pits, but it does knock the sharp edges off them and reduces their tendency to collect lead and damage subsequent boolits. The barrel will start off speckled and dark with deep pits and finish with shiny areas and the pitting more isolated and somewhat shallower.
Clover 320 is my "go-to" size. With the boolit coated and embedded with this material and seated in the throats with tweezers and dowel, a single case is reloaded and fired, with appropriate cleaning in between. I have fired 40 or 50 shots in a morning, with cleaning every five, checking for improvement with my "best" previous load, and come back several times to do the same thing until I figured that the barrel was as good as it was going to get.
I'd like to see somebody turn a .30 caliber barrel into an 8mm or .35 barrel by fire lapping. Not by sitting and watching, just by checking back every five years or so.