Gentlemen,
I have lived long enough to have seen a double shotgun gun convereted to a double rifle. It was an L. C. Smith. The fellow built a pair of barrels chambered in 30-40 Krag. He did a beautiful job. The receiver of the gun cracked and one lock plate was practically blown out. Nobody was seriously injured. There were two problems. One is that the action was never meant to stand the pressure of a rifle cartridge of that type and the other was the firing pin hole was a little to large for rifle pressure. In most shotguns the openings are pretty generous. The primer blew out around the firing pin into its opening. This especially true in the Stvens 311 and Savage Fox model B's. Be careful!
You might save up and buy one of the replica double rifles in 45-70 caliber. There you would not to worry about losing an eye or part of your face.
