The swastika was used by the Swedish steel manufacturer Sandvik as a quality control label until about 1940. I have no information about when they started using it or why. It may have predated the time when it was adopted in Germany. However, it is worth mentioning that, before WW2, many conservative Europeans did not at all dislike what was going on in Germany. Only after the war did the swastika become a totally unacceptable symbol because of its association with the cause for, and the events during WW2.
There is a book (in Swedish only) about Husqvarna shotgun manufacturing between 1877-1977. The information it gives about the markings on this barrel says that the swastika is a “steel quality label, company label, which was abandoned during WW2” (The Sandvik name is not provided). The stamp in the upper left corner is the pressure proof mark. The “P” is the mark of the assembler, Carl Petterson. He was active between 1902-1955. 18,5 means 18.5 mm bore diameter before the choke. The word “CHOKE” means that the choke is full. The model 103AS is pretty rare; only about 700 were made.