Your two cents are valid. It is just not the selling of shotgun action double rifle of concern; it is the personal liability what happens later while the double rifle is in use by the person to whom sold it.
In my case I wanted to learn how to build double rifles and regulate them and also to build a set of shoe lump barrels and from what I found while building them was that I could not find any other person in the USA who had ever built a set of shoe lump barrels.
As to the double rifle barrel regulation: setting the muzzle convergence when you braze the barrels together at the breech end is very, very important for ease of regulation later. In shops such as Holland & Holland the double rifle makers have recorded what the barrel convergence should be for all the calibers they have ever made.
Purchasing a Italian Rizini double rifle made with monobloc barrels is very inexpensive.
https://www.rizziniusa.com/rhino-express/Stephen Howell
