A man brought an old Damascus double into the shop one day, telling everyone how strong it was and that he had no problem shooting modern loads in it. I advised him very strongly to hang it on the wall. A few weeks later, he came in with a bandaged hand, and I asked him, "How many?" He knew what I meant and told me he had lost two fingers and part of a third. He told me, "I wish I had listened to you."
Not only are those barrels weak, but the pressure curve of smokeless powder is different. Black powder pressure peaks early, but smokeless pressure stays high past the thick part of the barrel, and it is at the point where the barrel thins that they usually let go. Of course, that is right where the shooter's hand is, so when they do go, pieces of the hand often go along.
Tuner is speaking the truth and deserves listening to. I have sectioned some of those old barrels that blew up, and while the outside looked good, the inside looked like Chantilly lace. The barrels were so raddled with rust and corrosion that I easily punched one through with an awl. But just looking at or looking through the barrels, they seemed OK.
Jim