Here's a piece of billet I just finished. It weighs 47#. We took a piece of end cut from a mill, turned it to get it round then wrote a cnc program to put the dome on.
Polishing was done with 400 800 1000 papers,Mothers power compound and a fast and slow buffing wheel.
It's about 60% complete in this pic.
Polishing is all in the prep, getting welds smoothed and not going to polish untill you've really worked the piece for smoothness.