No. An auto barrel is measured from breech to crown. The entire length of the chamber is included.??? how does a 6" barrel turn into 7.5"??? Is the auto not measured from chamber to crown?
A revolver barrel is measured from the forcing cone. So the revolver measurement "sandbags" not only the chamber, but the throat as well. So even if you measured an auto from where the rifling starts, it still wouldn't be apples to apples.