Team.
I have read Reynolds and Stratton and browsed Skennerton but can not find out why the two groove barrels had the rifling cut so much deeper than the 5 groove tubes.
5 groovers seem to have been cut .312-.314 for the most part but 2 groovers are .316-.318 or MORE.
I suspect the deeper rifling may have been to prevent over pressure of the same diameter bullet going down a barrel with less internal capacity. What say you?