How is the 410 normally loaded heavier than the 28 gauge? I have a bunch of 1 oz 28 gauge cartridges around. The heaviest I can recall seeing in 410 was 3/4 oz. But in any case same weight for same weight the 28 has the larger bore.

As for the 20 gauge, I believe I said you could buy cartridges for it that were not overloaded. Something not tue of the 410, and if it were true you would have a load like a revolver shot load.

As for column length I'll have to go think a bit. A nominal 16 gauge round ball would weigh 1 oz. If you stack small balls in a cubic array they occupy the same volume as one large ball of the same weight. Settle to smallest volume and it will have the same or lesser volume. A 1 oz shot column should have a length the same or less than the round ball. Is Herc including the wad or soemthing? The math doesn't add up.