Thanks Jimro.
Fascinating paper, I do not claim to understand all of it but pages like the following does a great job (I think) explaining why the point of impact can be so different with different bullets even if the powder charge is the same. No such thing as a (true) straight line from point A to point B for bullets.
http://www.nennstiel-ruprecht.de/bullfly/fig13.htm
Reading that paper and looking at ballistics charts for different calibers it is close to mind boggling that long range shooting is possible and predictable
