None of the above will predict where patterns will land when the gun is actually shot. The reason is that recoil is not factored into the deal. Recoil is what causes side by side guns to need barrel convergence. And, different loads will cause the patterns to "over-converge" or "under converge". When the right load is found many guns will converge properly, printing right and left patterns dead on top of each other. Then, the gun is regulated, with that load. Regulation of side by side barrels is a complicated affair and subtle changes in loads can affect that regulation boldly.
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