I wish you all the luck in the world with your project, but I have tried the laser trick in the muzzles and it didn't help out much. I know that putting a laser in at the breech end will tell you nothing, the barrels are bent slightly when the gun is built, (not enough to affect reloading though), and because of recoil and the twisting of the barrels around their center of mass when each is fired, the bullets won't go where the lasers point. To even get the points of impact close, the lasers would have to be lower than POI and crossed to each other to get the POI's close together.
How much? That's the golden question.

There are numerous things that affect regulation, recoil, elapsed time of the bullet while still in the barrel, gun weight, bullet weight, barrel configuration, wheather it's an OU or SXS, and MOON PHASE. Just joking on the last one, but after you have done a few of these, you would just about swear that anything can affect the regulating of a double, and you wouldn't be far off!

Here's a valuable hint if you will: If it is a side by side, adjust the barrels to shoot at the same height first, then adjust the in and out on the same horizontal plane. If it is and over and under, adjust the right and left adjustments first, then get them converging together up and down last. In other words, do the spread between barrels or convergence last. You will have to make several adjustments anyway, and some times they won't all fall into this rule, but as a general rule, this works out best. Bob H.