The whisper range of cartridges is what first grabbed my interest in the subs. All the reports are that they are capable of sub MOA accuracy out past 600m and some are still viable out to 1000m with very little loss of velocity.Thats why the whisper family is such a conundrum of a round it turns conventional ballistic thinking on its head, a slow heavy bullet shouldn't do what it does.
It would interesting to see what sort setup was used for testing that sort of ammunition out to 1000m.