Don't forget that when a set of barrels are joined for a double they are usually "Jointed" in to one another, IE they had flats filed where they join so the wall of each barrel is actually thinner on the inside than the rest of the way around. They are thus somewhat dependant on the fit of the other barrel to reinforce them at that point. Any amount of metal you remove as in sawing is going to reduce that thickness even more.
Why not leave them intact & do a Really Great project A Flint Double. Just a thought.
Pay special attention to what Miller said. He is absolutely correct. It most likely has a dovetailed lump and separating them by any means will result in significantly weaker tubes.
