History vs current practice.
O'Connor and others wrote about the 25 yd testing distance for the .410. Interestingly, Jack said the 25 yd standard was for a 24" circle (not 30"). I can believe that, as a 70% pattern in 30" at 40 yds was not going to happen with Pb shot through a "full" .410 prior to shotcups. My pre-1950s "mod" M-42s are surprisingly lightly constricted, averaging only about .006". Not a chance you would get a 55-60% 40 yd pattern out of them with fiberwad loads. 25 must have been it.
But just as interesting as history are the revisited patterning capabilities of modern .410 loads. My M-42 "full" gun (.016) that should have given 70% in 24" at 25 yds "back in the day" now gives 67% in just 20" at 40 yds with RP 3" #6. Kinda like night and day.
Choke is definitionally a percentage, and not dependent on pellet number. So 2.5" shells do better, albeit pattern density suffers. The shot in 2.5" shells benefits from full petal protection and, of course, the shorter column height.
Guess I'm saying that .410s can now run out of effective pattern before they run out of choke. You can pattern them at 40 yds with good shells, get some respectable percentages, but still not like what you see......b/c half an ounce ain't very much.
Sam