The issue of regulation of double barrels evokes lots of verbiage. In an earlier time the makers of fine shotguns would regulate their guns to owner's specific cartridges and loads. This info would be supplied with the gun when delivered.

DR makers still do that and every new DR comes with a test target.

The effects can be seen most easily with DRs since there is only one hole but it's the same for shotguns.

There's a lot of nonsense on the SGW thread such as the claim that double rifles are for dangerous game so they have to be accurate. No DR is as accurate as a good bolt-action. 4 or 5-inch groups at 75 yards is pretty good for offhand shooting with a DR.

Properly regulated barrels never cross at any distance.