The 28 gauge patterns efficiently because its ¾-ounce payload is “square” (inasmuch as anything packed in a cylinder can be square), according to conventional shotgunning wisdom. Theoretically, the 28’s squareness results in less-deformed shot, because as the payload accelerates, there’s less weight on the pellets at the bottom of the stack, so they stay round and pattern well.
Except it isn’t square. “Square” means the shot column inside the hull is as wide as it is tall. Or, if you’re talking about blackpowder, it means equal volumes of powder and shot. Under neither of those definitions is the 28 gauge is square.
The 28 has a bore diameter of .55 inches and a shot column that’s about an inch in height, and “volume of black powder” isn’t a useful metric anymore. The 28 is a rectangular load, if there is such a thing. And, given improvements in shot that resist deformation and wads that cushion shot and protect it from scrubbing by the gun barrel, the idea of a square load may not matter as much as it used to.
Squareness aside, a lot of people are convinced the 28 gauge is magic anyway. That includes plenty of experts, lots…