This is my "Personal" opinion without extensive data to back it up. I do think however that much of this idea about long column loads giving poor patterns arrived from the very early days of smokeless powders when all available shotgun powders were of a relatively fast burning nature. Any attempt at heavier loads resulted in higher pressures, possibly even dangerously so, & likely did give a "Hammer Blow" to the shot column with resultant deformed shot & poor patterns. The development of progressive burning shotgun propellants however in the 1920's allowed heavier loads to be used with no increase in max pressure & did away with the overly sharp rise of pressure. Loads that are "Beyond Square" have been used successfully ever since. Prior to this the Square load was mostly applicable to only the 10 & 12 ga's. This was pure co-incidence as the length of column capable of being handlled without Excessive deformation just happed to work out to be of the approximate length of these two bore diameters. 1 1/8 oz has "Always" been a very practical load weight for a 12ga & it was a bit beyond square, having a column length of about the same as a 10ga bore diameter.Even with the early powders a pretty good 1Ľoz load could be used in the 12 if one didn't insist on maximum velocities. & this was definitely beyond square.
