Felix,

The Rail Revolver command will only produce a result with a flat edged surface, as it is a revolving sweep that simply scales the profile to match the rail as it is revolved.

A workaround can be done with a "two-rail" Sweep.

Use the shape you drew on the bottom, but place a small arc or circle on the other end of the profile shape you want to revolve.
Sweep, after choosing both rails, will then make the new surface conforming to the desired rails.

Hope this helps.