I have never quite been able to figure how to fire a "Square" load down a "Round" bbl.
Actually I believe the "Original" definition of a square load was one in which the shot column had the same length in the bore as it's dia, while one which weighed the same as the round ball, was simply a round ball equivelent load. A square load can thus be fabricated for any gauge desired (volume for a cyl of L =D is ~Dcube/4) Volume for 1oz of shot is a nominal (varies according to exact size & alloy) .288 cuin. One soon sees the Sq load is useful mostly in the 10 & 12 ga's being approx 1¼ & 1 1/16 oz respectfully.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra