Each barrel's line of sight with the rifle at rest, as in a vice, with the sights lined up on an aiming point at any given distance will not be pointing to the same place, nor will it be pointing at where the sights are pointing!

Thinking that is the problem with most trying to regulate a double rifle during a build, or working up a load to shoot to the regulation that is already built into the rifle!

To see this for yourself take the barrel set from a double rifle that is known to be regulated properly. Place the lumps in a padded vice, and support the forward end of the barrel set so that the sights are aligned on an aiming point at the distance engraved on the standing rear sight. Most big bores will be 50 Mtrs most small bores will be 100 mtrs. Now take two empty cases, with the primers removed, and place them in the chambers. Look through the primer holes in each case and see where that barrel is pointing on the target in relation to the aiming point, and with the other barrel. I believe when you do this a light will come on in you mind!

With the sights being held in line with an aiming point on a target, no matter the distance, the RIGHT barrel will be looking at a point the is LOW, and in the LEFT of the point of aim. the LEFT barrel will be looking at a point that is LOW and on the RIGHT of point of aim on the target.

This is necessary because when the barrels are fired with the sights lined up on the target, the recoil will move the barrel being fired UP and AWAY from the other barrel, before the bullets exits the muzzle. This is called barrel time. So the barrel is not where it was when the trigger was pulled, and because of barrel time, the barrel is at a place that is at the right elevation, and pointed at a point just BESIDE the point of aim, on it's OWN SIDE of the aiming point on the target. The barrels have to be physically converged, with the line of sight crossing, so that the barrel will be shooting SIDE BY SIDE when they get to the target. Contrary to popular belief, a properly regulated double rifle shoots its barrels parallel, and the CENTER of each barrel's individual group never crosses at any range.

The only thing the Laser will give you is a starting point to begin regulating the barrel set when building a double rifle, but you have to have an educated guess at a starting point, and you never want to make a double rifle shoot in the same hole with both barrels. If you do the barrels are crossing, and the will get steadily wider as they go down range. This is not correct, the barrels should shoot side by side, close or down range!