When they figured out how to mount two barrels, side by side, with two separate firing mechanisms, and the barrels indexed to the same point of aim at a predetermined yardage, they reached the apex, the epitome of shotgun technology.
Anything since then is just useless piddling.
Ah, it warms me heart. It does.
ye olde grouse hunter.
And yes, the O/U...a simple revolutionary change.