If I remember correctly, the 168gr bullets was originally a designed by taking one of the .50 CAL bullets and downsizing it to .30 cal. The result was a 168gr bullet that has been a standby ever since. The Germans did just the opposite with designing the V2 rocket. The base shape is a 8mm Mauser bullet (192 grainer I think) made really big with fins plastered onto it.
Can't really speak for the 168's but 154 and 139 are 9 and 10 gram bullets so they convert easily for the rest of the world especially for the metric calibers