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.
smy1, I'm glad a fellow Okie posted this. On a lapped custom barrel the throat from chambering will have a little machining fluff. My break in procedure is a small amount of xxxx steel wool wrapped around a bronze cleaning brush and with a hand drill lap the throat for a few seconds. Run a wet and dry patch through it and you are done. I haven't had a factory barrel in years, so can't speak of them.
I don't know any custom maker that laps any finer than 320 as a polished bore will copper foul moreso with a slick bore.
Now in a month or two another thread will spring up again on this subject.
