There were multiple reasons makers recommended not shooting nitro in black powder guns and Damascus in particular. First is that nitro ended up being loaded to higher pressures and higher velocities. Maker did not want guns designed for 6,000 psi shooting 8,000+ psi loads. Second there were so many different grades of barrels materials that no one recommendation covered them all. Third if they recommended to not use old guns it stood to reason that you would need to buy new ones. Hence sales drove the advise in part as makers like selling guns and staying in business. The funny thing is that the gun does not care if the powder used is black or nitro. Only the pressures matter in the end.
