Cool picture of the Rigby "High Velocity" cartridge. Unfortunately, no evidence that the cartridge shown is what that rifle was set up for. From another source, apparently the 100, 200 and 300 yard sights suggest 173/175 grain loading. (1924 Rigby Catalogue) Would have been 100, 300 and 400 yard sights if it was for the High Velocity, and then would have had the engraving on top of front ring to indicate that - not evident in the pictures from the OP. Is also possible to be a "Ladies Rifle" - would have had slightly shorter barrel with about any choice of sights.