I've always thought chrome lining might be a solution to this problem. I don't know much about the process. If it was feasible it would already, probably, be being done. Any thoughts ?
Sure. Hard chrome plating the inside of pitted shotgun bores would involve first machining out the pitting, as was done in the case of the high dollar aircraft struts mentioned above. You cannot fill in pits with plating, and get a smooth surface. Then the bores would be nickel plated, followed by a hard chrome plating of not more than .005". Going any thicker would lead to problems with the chrome surface, which is much more brittle than steel. I can't imagine that .003" to .005" of chrome plating will make the barrels any stronger, especially if you honed out that much or more prior to plating them.
I have no idea how this would be accomplished on an intact set of double shotgun barrels, i.e., how this could be done without plating the outside or affecting rib solder joints, etc. This may have been economically viable on high dollar aircraft struts, to prevent future internal corrosion, but likely wouldn't make any sense whatsoever on a set of old pitted shotgun barrels, unless the gun was rare and very valuable. Anyone want to speculate what sort of valuation hit a Parker A-1 Special or Lefever Optimus grade would take if you chrome lined the bores???
The idea that any currently available epoxy as a bore lining would have merit would be quickly dashed by simply taking a sample of the epoxy and comparing the surface hardness to the hardness of typical shotgun barrel steel. Then compare all of the other attributes of steel that make it the universal choice for gun barrels. It is wishful thinking to believe that an epoxy lined bore in a shotgun barrel would last, given the temperatures, pressures, and friction involved. Even when these materials are used to repair pitted surfaces in a cavitating centrifugal pump, for example, the repair is regarded as a temporary fix until a replacement can be acquired.
If I'm going to dream about something, I'll dream about winning the Powerball Lottery Jackpot, and then buying a really nice shotgun without pitted barrels.