For my last new barrel, I cleaned the rifle after every shot for 20 rounds. Thereafter It was sometimes cleaned after a group if I was at a range for checking zero, or after each hunting trip. Don't know if it was necessary or not.

Incidentally, I always use a dry patch, followed by a patch soaked in lighter fluid, followed by a dry patch before I start shooting in order to remove all traces of oil in the bore. The theory was that a) the lighter fluid evaporates (being flammable), b) any residue is much finer than machine oil (therefore less damaging than oil if left in a barrel when the bullet is fired) and c) most of the lighter fluid residue would be removed by the final dry patch (not the case with oil). This was part of the drill that we used when I shot competitively at Bisley - we were coached by a member of the GB match rifle team. I thought everybody did it, but apparently not!