If you are using a custom barrel that has already been lapped by the maker, the only tooling marks left are in the throat from the chambering reamer/throating reamer. Those will be smoothed out by any of the already mentioned procedures. If you want to smooth out the throat before shooting, a little JB (the light brown, not the red) on your choice of mop or patch applied in and out a number of times through the throat only, followed by a cleaning of the full barrel will do.
