Ok Dogleg, when everyone in the west was picking 30 and upwards for their military rifle calibres only a few thought about the ballistic efficiency. Penetration was what it was all about, add the stability in flight right out to volley fire distances and you get the perfect round. The wise countries were the swedes, the japs, the US navy and the Italians. The stability of a bullet is enhanced by the mass of the bullet being wholly or mainly retained in its cylinder section. This is why a longer slim bullet is better than a big fat one!
The Spanish and Soth Americans, Boers etc came very close with the 7mm Mausers. They werent the best battle rifles but certainly were amongst the most accurate!
The penetration part is a bonus in the play off stakes with stability, if you use a tungsten core dart or DU penetrator core then you can cut through just about anything out to spectacular distances. The balance needed here is that of imparting energy to the target so it will roll over and die!
Tanks etc brew up when penetrated by such dart ammo but a balanced wound is needed for flesh.
The sectional density is part of the equation, match that to a good ballistic co efficient and you should have the ideal round. Obviously then you need to get that round to travel the distance you want. sadly the 6 and 7 mm arent cut out for very long range work so thats where the 338 etc comes in!