Also, refer to information on Dutchman's excellent web site ..
"The most common of the bore discs. The range of numbers from 6.46 to 6.59mm refers to the diameter of the bore. The increments are very nearly spaced .0004" apart, or 4 ten-thousandths of an inch.
This disc is marked at 6.52mm. The pie-shape with 1-2-3 refers to the amount of -rust- observed in the bore, though I've never seen -rust- in the bore of a Swedish Mauser. This disc is marked a #1, which is better than #2. The Swedes had certain standards for acceptable wear in their rifles, but it's almost unheard of to see a Swede barrel that's worn out.
The lower section is mostly unused. "Torped" refers to the boat-tail 139gr m/41 bullet. "Overslag" refers to over shooting, and the "str" is abbreviated for streck. There are 6300 streck in a circle. One streck equals .1m at 100 meters. This is really an indication of how high a bullet will strike the target in relation to point-of-aim."
Swedish Butt Discs