.615 is nominal 20 ga so @ .617 Win was using a .002" overbore. Measuring "Just the Choke" is never of any value at all, the bore also has to be measured to determine amount of constriction. Bores varied all over the board from Nominal, even among guns of the same make at different points in time.
When used as a % of bore reduction .025" in a 20 gauge is = to .030" in a 12ga. In the old days of card & felt/fiber wads this was considered IM, but with modern plastic obturating wads with shotcups it is considered full.
