The guys nailed it.There's as much variation from shell to shell in a box as there is in 8" more or less in a bbl.
Frankenstein, my overpublicized parts 870, has been used on snows with good results, tho some blind mates aren't fond of the blast from its 21" bbl. And flash in low light is impressive with 3" mag goose loads. But, the geese do not seem to care.
24-26" of bbl on a waterfowler will not change velocity or range.