In the autumn 2009 issue of "The Double Gun Journal", there's an article in which a number of these old shotguns were tested with modern 18,000psi "proof" loads. There were no failures. Any barrel can be unsafe due to horrible pitting, cracks, or obstructions. Older barrels are more likely to have these defects, but so often the failure is wrongly blamed on the material not the defect. It is common in Europe for vintage guns with damascus barrels in good shape to be retested a proof house and approved for modern smokeless loads
It is not worth my hands or head to shoot these old relics. There are plenty of pictures on the web of injuries with firearms. I don't plan to add to them.