Before I say what I have to say, let me be clear, I AM NOT AN EXPERT. I bought my first double rifle a year ago, a Henry .500 BPE. I did a lot of research on loading for this rifle and what I found was several sources that claimed that the barrels were regulated by powder charge. If the shots are going wide, increaseing that powder charge will bring them together. If they are crossing, lowering the powder charge will bring them back together. It was recommended to start on the lighter side (which should make them shoot wide) and increase the charge until they meet. My initial thought was "How the hell does THAT work???". But, I found the same recommendation in several different places. So, I made up several loads of increasing powder charges and found that the first ones shot rather wide (@ 50 yards) and as the powder charge increased, the shots came together, just like I was told. For the record, I am using smokeless in place of black but my understanding is that the same principle applies for black. I can to wrap my head around WHY this is how it is but my initial limited testing seemed to conclude that this may have merit.