there is not problem with a drilling that has two shot barrels, and one rifle barrel below! The laser will work there because the drilling is simply a single barrel rifle that happens to have two shot barrels on either side and above the rifle barrel. You simply solder the shot barrels together so that the patterns over lap each other then solder the wedges on the rifle barrel so that it point to the center of the pattern but a little low of center. Then mount the sights and cut them to print the rifle where you want it at 100 yds, and hold over for longer range as you would on any single barrel rifle. The single barrel being in the middle of the firearm, it recoils back, and up only, so all one has to do is cut the sights. no regulation of barrels are needed. The same pertains to an O/U combination shotgun, and rifle!

Double rifles are a whole ball of wax unto it's self, and requires a regulator who knows what he is doing. This is why you need to always take a double rifle to a double rifle smith. Most single barrel shooters simply do not understand how a double rifle works, and 99% of the gun smiths know even less about them. However that fact doesn't hinder everyone haveing an opinion about how they work, even if 90% of them are wrong.