Just a final followup. After some e-mail exchange with Chuck Hawks, the consensus is that the two rings on the disc are actually to be read as one range. Going from small to large, the inner arc starts at 6.46, then 6.47, 6.48, 6.49, 6.50; at that point, the series shifts to the outer arc for 6.51, 6.52 and so on to 6.59. Actual gauging would have started with the highest number (largest gauge). If that didn't fit, they would go to the next smaller. When one fit, that was the number marked on the disc with a triangle.
But, as Wildalaska says, no matter what the markings meant in Swedish service, they mean little today, especially since many of those rifles have been in this country since about 1960.