Thank you for this. Very interesting to know what these markings mean. Regarding the Ch 15, I thought at first that this might have been an accidental transposition of Ch 51. But that wouldn't make sense unless the "1" and the "5" were applied in different steps.

If this were either an "S" or a "J" bore, what markings would you expect to see where the 7,85 and 8,15 are now?

Regarding the 'renumbering' generally - I learned from a South African friend that some sporting rifles were renumbered by authorities as a result of gun control legislation passed in 1937 in that country. He thinks it could be related to that.

Do you think it would be safe to fire an 8x60S RWS cartridge if it will chamber in the rifle? (with appropriate precautions of course!) I can get 8x60S ammo but have no idea where to find 8x60.

Thanks again.