I dunno? Never seen any figures regarding accuracy and percision regarding various barrels.
Mostly its from experience. If you can get yoor hands on a freak kit then shoot some paint with the biggest insert at a traget a reasonable distance away, (50-60ft should do). Now use the correct correct sized insert and shoot at the same target. Magic!
Also, most stock barrels are .689 to my mind, so if you're shooting larger bore, like polar ice winter paint, it will break midway down the barrel. better to use a larger .693 or .695
hope this helps