Larry;
no mystery involved here at all, it is pure mathematics.
Well, we certainly agree that the 28 and the 20 are more alike than the 28 and the .410. You don't really need any math to get there. Well, maybe a little . . . enough to tell that the 20 and the 28 are closer in bore diameter than are the 28 and the .410.
But, assuming all you say is true, this still seems at least somewhat mysterious to me: not only does the 28 have a smaller bore, meaning that the shot is more likely to deform (assuming equal protection furnished by wads and equal hardness); but the 20, in its standard skeet load, has 1/6 more pellets (7/8 oz vs 3/4 oz) than does the 28. Yet the skeet averages quoted by Brister are virtually identical. About 1% difference. Seems to me the 20 ought to show more of an advantage than that.
