You regulate a double with solder, a torch, and wedges..regulation is done at the factory...

You adjust it by firing different loads until they come together as a group that equals the 4 shot group of the "worst" barrel and this gives you the accuracy potential of your particular rifle, it will shoot no better than the "worst" barrel...(group both barrels seperately to start with)

Then you sight the rifle in by movement of the front and/or rear sights....