The barrel walls
must be measured. The gun should be inspected by a gunsmith who knows old doubles and has the tools to do a proper inspection. Any signs the barrels have been honed should be examined closely.
This is a 1891 example of recommended barrel wall thickness. It is a good example of the points that need to be measured.

The pressure should kept at or below 7,000psi. Low brass is NOT low pressure. The loads should be kept below or to 1 1/4 oz.
Almost every example of a blown damascus barrel I have seen can be traced to thin walls, barrel obstructions or high pressure loads. I shoot my damascus guns with both black powder and low pressure nitro.
Pete