As I understand it, (and I certainly don't claim to be an expert) the issue of using smokeless loads in these old shotguns is not one of "maximum" pressures, but rather one of the so-called "time / pressure spike" which is totally different with the smokeless. The gun may handle a few modern shells with no apparent problems, or it may not, but I would never take that chance...I just don't see the risk as being worth it.

If the gun checks out after examination by a gunsmith who knows what to look for, I would, however, have no hesitation about shooting it with some moderate black powder loads. Given the proliferation of western style shooting these days, you may even be able to buy black powder shells already loaded. (?) Be sure to clean correctly and well after the BP, of course.

 I have a very old double-barrel shotgun that has a “tiger stripe” or “swirl” pat

 Question
 I have a very old double-barrel shotgun that has a “tiger stripe” or “swirl” pattern on the barrels. What kind of barrels are on this gun?

 Answer
 If you have a noticeable, and often ornate, pattern on the barrel or barrels on an older shotgun, chances are that you have Damascus barrels on the gun. The pattern on Damascus barrels was a result of the manufacturing process. The term “Damascus” refers to a welding technique. The barrels were a product of layered steel and iron strips that were heated and forged together, then twisted in a lathe-type device, then heated and twisted around a mandrel while being hammered and welded. We would strongly discourage you from attempting to fire this gun as these barrels were not built to withstand the pressure of modern ammunition and could “unwind”, thus creating a safety hazard