AhHa the old Square load rears its ugly head again. I have also read that the 3/4 oz load in a 28ga was the Perfect Square Load. He based this by saying (incorrectly) a square load was equal in weight to the round ball which fit the bore. He then correctly stated this could be found by dividing 16 by the gauge number. Thus 16/28 = .57, Thus the 3/4 oz load is "Perfectly Square" i the 28 gauge. This hogwash was written by a highly published & well known writer of things relating to shotguns in particular. Even an ole Redneck Hillbilly like my self knows that even though they contain the same two digits .57 & .75 "Ain't The Same".
In reality the old accepted square load is one in which the shot column in the bore is equal to the bore diameter. Thus in 12 ga with a .729 bore & column length of .729 the load will be approximately 1 1/16oz, heavier than the 2" 12 is normally loaded to.
For the 28 gauge with a .550 bore stacked .550 high the load will be just a bit over 7/16 oz, 29/64 if you want to split hairs.
The only gauges which in the past have been traditionally loaded close to a square load was the 1 1/16oz British game load & this came about as an act of parliament I believe for the purpose of saving lead during WWI. The other was 1Ľ oz in the 10 gauge which for many years as a very popular load. Most other gauges were traditionally loaded "Heavier than Square".
The square load Theory truly needs to be buried deeply in a hole (Octagon Perhaps) & be sealed over so securely it can never again escape. It is absolutely of no benefit.
It suffices to say that original loads were loaded with same shot charge as 20ga, but were later increased to mimic 16ga game gun loads because cartridge pressure of former was not sufficient to give good results. I would think while not as common 12ga 2.5" guns vintage 16ga gun when found would be less costly to buy therefore preferable to paying premium for 2" version.
