The regulation of double barreled guns has fascinated me for many years, mostly that of shotguns, as opposed to double rifles. I became aware that not all double barreled shotguns are properly regulated with just any old load early on. Some cannot be found to print the individual patterns atop each other with ANY load but often, when a side by side shotgun crossfires, all that is needed for perfect regulation of the patterns is to try different weight payloads and velocities.
This is just personal observation, but most often when one cross-fires badly it is because the payload is too light and/or the velocity too high. The last example I ran into is my dedicated quail and woodcock gun, a Philadelphia Fox 20 SWE. I wanted to use 7/8 oz. loads in it so when I first patterned it that's what I tried. They were running at about 1200 fps, as i recall. To my chagrin it cross-fired to the tune of 8" at about 20 yards, equally so with both barrels. I was sick when I saw that. Turns out that all it wanted was 1 oz. loads at about 1150 fps to put those sweet patterns right on top of each other at POA.
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