I have a black powder proof Belgian gun (Francotte) that I shoot with nitro loads mostly of my loading. I keep the pressure under about 600 PSI for my loads. Generally 4500-5000.

I had the barrels checked by a good gunsmith, then x-rayed at my friend the physician's office. Then I had the barrels checked by an aircraft mechanic...I've forgotten the coating process.

There were no defects shown in any test so I continue to shoot 7/8 an 1 ounce loads in this 12 bore. It was made in 1891-1892.

Fiocchi makes a trainer load for 12 gauge...7/8 ounce that is according to the factory between 6500-7500 psi (probably less). It may be a good starter load for damascus barrels in otherwise perfect condition.