I know a guy who could point out a problem with all that, except that he couldn't do it with his left hand since he has no fingers there. They departed along with a big chunk of a Damascus barrel when he insisted on firing modern shells.
Here is the problem with firing ANY smokeless powder loads in those guns. Black powder expends all its energy very quickly, so the high pressure remains in the thick part of the barrel. But progressive burning smokeless powder keeps the pressure on beyond the thick part, and there is still high pressure out where the barrel metal thins down, which is just where the shooter's off hand is holding the gun. The chamber pressure is the same, leading to the idea that there is no difference, where there is.
IF you think you can tell for sure that a Damascus barrel gun is safe, obviously you know more than I do. But IMHO, anyone who claims a Damascus barrel is as strong or stronger than a good modern steel one is under some serious delusions.