Allen, it comes from simply being fact! However, what I think confuses even those who are well up on double rifles, is the misconception that saying the shots from each barrel do not cross at any distance! This "IS" wrong. What should be said if the "CENTER" of each barrel's group do not cross at any distance! A group fired from any barrel will get larger as it flies down range. If there are two barrels side by side, as the two groups get larger the shots on the right side of the left group will certainly cross over into the group from the right barrel and vice-versa. this only means the composite group of both barrels gets larger as it flies down range, but the center of each barrel's groups remains on it's own side of the POA!

Even if a single barrel fires four shots, all four will not het in one hole, and if that barrel is fireing a MOA at 100 yds, it will be 2 MOA at two hundred yrds, but the center of the group will stay true to aim! This is why the mistaken idea that multiple flip-up sights on a double rifle are simply there for decoration, and they are not, if the rifle is loaded properly to the regulation of the rifle it wwill shoot to those sights at the range they are set for, and you will notice all the centers of those sight baldes are in line with each other!