You get the best patterns with shot loads in Black Powder, cylinder bore guns when the velocity stays below the speed of sound. That is why " magnum" is not a friendly term. More powder simply blows patterns.
The round ball has a terrible Ballistics coefficient, and most shooters can easily accept that shooting a single RB from a smoothie, or rifle. However, most don't consider that air is not only dragging on the back of each round pellet in a shotgun load, but its also pushing the pellets apart. There are pressure waves created by going above the sound barrier, off the nose and back of each pellet, and the turbulance created forces pellets apart faster.
Since its difficult to get ABOVE sound barrier velocities with Black Powder, anyway, because of the slow, progressive, burning character of this powder, keeping the MV under that SPEED OF SOUND is the most practical way to get better patterns, and more pellets on a target. If you want more energy down range, you use a larger pellet size, rather than attempt to get it by speeding up the load.
You are, in effect, "reloading" a new " cartridge in the barrel EVERY TIME you load the gun. There are no physical limitations to shooting more shot pellets, as there are in all modern cartridge casings, so you can simply increase the volume of shot in your load to put more pellets on the target as the ranges increase.
An old Article from the predecessor magazine to the American Rifleman, from about 1880, showed a favored "50 yd. load" for the commercial Duck Hunters on the Illinois river at that time was 1 1/4 oz. of #5 shot, over 2 3/4 dram( 75 grains) of black powder.(12 gauge shotguns, both MLers, and the early Breechloaders.)
That load has a MV under the SOS. I have used the load in both my MLers, and, with a smokeless powder equivalent to that powder charge, in my modern choked 12 gauge shotgun. I have killed pheasants with my cylinder bore MLer out at 33 yds. With the modern equivalent in my choked barrel, I have killed pheasants way past 40 yards with the load.
The ducks were shot as they flocked together on the water, and not in the air, but this was how they could maximize their kills to sell ducks to the restaurants in Peoria, and to dealers who transported the ducks by rail to Chicago in early refrigerated RR cars. Ducks were sold for $.10 each back then. That was an hour's wage for most jobs at that time.
Commercial hunting was not banned until the early 1900s in all the states, with the passage of the Lanham Act by Congress and subsequent Migratory Waterfowl Treaties with Canada and Mexico. The States brought their state laws into compliance with Federal laws, by the 1930s, to benefit from Federal excise tax revenue.
All these changes took place as we moved from using ONLY Black Powder in MLing shotguns, to using smokeless powder and breechloading cartridge guns, and finally using barrels that were choked at the factory. With Smokeless powder and choke, patterns could still be made at longer ranges, with the smaller shot size and shot loads that the restricted length of shotgun cases imposed by generating speeds above the SOS. The appearance of plastic shotcups in the 1950s allowed the higher velocity loads that so many shooters have used, and come to expect as " Necessary" for hunting any kind of game.
