If it bothers yo find a steel ball bearing that has about the same radius or curve of your current crown. First hold some 320 or similar emery cloth tight on the bearing and rub it around on the crown working in multiple directions. Then go to an auto parts store and get some course valve lapping compound. Coat the muzzle and roll the ball in random patterns. Eventually it will get polished.

But, here is an interesting fact. I have cut down a few different barrels. I of course wanted a factory looking crown. In studying my S&W crowns from my 44 top break to my latest there is nothing uniform about them, even in guns of the same period, finish, angles and radius all a little bit different from one to the other. How they transition from barrel to ramp etc. I have a little pile of barrel stubs I keep around just for comparison when I am working a muzzle on my lathe.