I read on the internet that the steps could not be removed because a straight taper would make the muzzle way too thin.
This was years after I had tapered a barrel for a school mate. I set the taper for each section( by setting over the tailstock) to remove that shoulder, then did the next section. That gave three straight tapers that I then filed to blend them together. Looked good and the owner was well satisfied. Of course, I did not know at that time that it was impossible to do, as I had taught myself to use the lathe based on a Henry Ford School textbook. It was 4-5 years later before I got professional training as a gunsmith.