Charlie;
The theory behind the square load is that the longer the column the more shot are stacked up in front of the lower ones, closest to the wad so they are more deformed from the compression created by the inertia of the forward part at rest. If though a 12ga gun can with effectiveness use a column of .730" length, then if you have a column .860" long the forward .730" still has that same Square length as you said. It is as you have pointed out ridiculous to assume that every pellet in the lower .130" of the column are going astray & none of them will land within the pattern. This raises the load to 1Ľoz which has always been an effective load for a 12ga but is no longer square. Further if a 12ga will shoot a column .73" long why will not a 20ga or a 28ga shoot the same length, it will have the amount of shot stacked on top of the lower layers as the 12, though they are no lomger square simply because the bore is smaller.
