There will ALWAYS be sanding lines in a bowling ball. Until you can buy the abrasives used to buff precious stones likes emeralds and rubies, even with a naked eye you will be able to see sanding lines.
It is my belief that you can take this visual sanding lines preception to an extreme. 4000 grit is extreme fine for a bowling ball resin exterior. The only thing finer that I know of is Trizact white or Cerium Oxide pad. It virtually polishes the ball. Even a used 4000 grit Abralon will polish a ball, without the use of polish.
In order for the sanding lines to be RELATIVELY uniform in size and depth, you need to either use every intermediate grit sanding pad/device WITH LOTS OF WATER, on the way to your target or, even better, use a commercial sanding machine such as a Haus machine.
Polish will NOT smooth out the sanding lines UNLESS you use one with aggressive particles in it, like Brunswick's Rough Buff or Track's, now Powerhouse's Clean and Sheen or Ultimate's Quick Kut & Polish. Even then, you still better off sanding the ball starting from a base level, like 400 grit and work your way up.
Good luck, in any case.
--------------------
"None are so blind as those who will not see." Unofficial Ballreviews.com FAQ
