Swastika forms don't necessarily have anything to do with the "Thousand Year" Reich; it is, as the Nazis knew, a VERY old symbol with many meanings in many cultures (NOT about to get into that here; kinda OT....). It was used "locally" in Scandinavia by the Finnish Republic after their independence from Russian in 1917 and this Swedish gun might have some Finnish association.
But probably just a barrel-makers mark that I'm not familiar with.
I lived for many years near Troy, NY and was always amused by the rows of swastikas that formed a decorative border around the ceilings of its elegant (pre-Nazi) Post Office building!