The two barrels will have individual groups that should be super imposed over one another. This would be ideal. It doesn't happen very often. Every person holds a gun differently and thus the groups will vary in distance apart. A double should shoot each barrel in a group and the distance between the groups should only vary if the load varies. I big person that holds a gun tightly will typically shoot tighter than a small person holding the gun loosely. This is why you might shoot a better overall group than I do with a specific load. The loads can be adjusted to regulate for a specific shooter. Factory regulated guns are shot with a specific load under their standard conditions of firing the gun. This could be in a machine rest or held by a shooter. Most guns will shoot a good overall groups with the regulated load for most conditions. I have some doubles that will shoot individual groups of less than an inch and overall groups of 1.5 to 2 inches. This would be considered as good in my opinion. Others may have the two groups inside 3 inches. If a gun won't do that then the load needs to be changed. If the individual groups are all over the place and vary in distance apart then the gun probably needs to be regulated. That is if the person shooting it is doing their part. If a gun is out of regulation two shooters should get similar results.

Sam