What was describded to me was NOT that the actual total amount of rifling shifts to the outside of the barrel, but more like that a visible pattern appeared on the barrel surface which followed the shape and position of the internal rifling.
The suggestion was that the monolithic and some other solid bullet types were creating a swaging effect where over time and many firings with monolithic type solids, a small shifting of the barrel metal takes place.
The barrel does not end up with all the rifling on the outside and a smooth bore.
The barrel still looks the same internally but shows a spiral pattern on its outside surface which matches the internal rifling.