As a guy who has done a lot of shooting with a Sharps at unmarked distances, I don't see this as any big feat. If a person is used to judging ranges, it is not a big deal. If you shoot them enough, the trajectory is pretty much locked in your mind, how the bullet will fly. The sights are just gravy at that point. Any time I shoot a long range rifle, I can visualize the trajectory of the bullet pretty darn close, from firing lots of rounds down range. Something that has really helped, has been being a spotter for many years, and watching the boolit from just ahead of the muzzle, to all the way to the target. That teaches a person more about trajectory at different ranges than all the charts and graphs in the world can ever do.