Larry;
Maybe, just maybe you're starting to actually think a little, you do however still have a ways to go.
Consider however the 28 & the 20 gauges are much more "Alike" than are the 28ga & the .410. Anyone who "Expects" a major difference in the performance of the 20 & 28 simply have their expectations misplaced.
Discount the occasional shot made where a single pellet happens to luckily strike a vital spot at a range at which the shot should not have actually been fired. Outside this the effective killing range of a shotgun, assuming pellets having adequate penetration, is determined by the density of the pattern insuring adequate hits on the target, but I have no doubt you are fully familiar with this.
Staying with the same size of shot there are three ways of increasing this range, 1; a heavier load of shot, 2; A tighter choke & the third one is a pattern giving a higher rate of central core thickening.
As pointed out even though these various loads have been showed to have very close actual lengths of column (not including the .410) the length relative to bore is significantly different. This puts a higher % of the shot in bore contact. With soft, unprotected shot this is a decided disadvantage due to shot deformation from scrubbing & direct contact with both the forcing & choke cones, many still relate to that.
Many today have made the claim that firing good hard shot with a properly cushioned shot cup the effect given to the smaller bore is that increased central core thickening will give the small gun a longer effective range, even from a choke giving the same overall percentage. The price paid is of course a lesser diameter killing circle requiring more accurate shooting.
There is however no mystery involved here at all, it is pure mathematics.
