Curt, not a fan of firelapping. If the pipe is shooting badly or fouling quickly thus loosing accuracy, get another barrel.
A barrel that fouls but shoots well is not a problem. never judge the accuracy of a bore by how dirty it gets.
Firelapping only works on the throat area which is the LAST place you want to remove. Once the throat is moved forward so that a bullet cannot fully engrave before leaving the case neck, you loose all accuracy.
Firelapping is very rapid bore erosion.
If you really must, just some JB borebrite and have at it. Basically, jewelers rouge so will be mildly abrasive but you got to be at it a very long time to do damage. This stuff works nicely to take polish high spots on lands but isn't really designed to remove metal.
Jerry