It is true that a round ball is the poorest balastic shape, that and the fact the bigger round balls and the great heavy bullets are limited by the amount of recoil and the twist which is always designed for loads the "normal average person will shoot"
The combination of a 54 weight being in the range that allows reasonable recoil while pushing it up to 2100 feet per second so it end up haveing the best [flatest] trajectory that is available with a round ball, the other point is that it has more capabilityfor stopping medium size game, I now there will be some peole especally the ones that shoot loads like I put in the kids guns when they were little that will argue thisbut I have taken 27 deer several bear and 3 boar with a PRB in a 54; one deer I shoot a bit farther bach than I wanted and was out 120 yds and moving ran about 60 yds after being hit and one [very large bear] ran about 40 yds the rest were dropped in there tracks. Now we all know shooting them in the right place is necessary for good results so we wont go into that. I have my own idea of why it works so good, it takes a combination of caliber and velocity to drop an animal in its tracks with medium size game it is possable a .270 with a 130 gr bullet or a 3006 with a 150 gr bullet or a 54 cal with a PRB will do it. I have had to track a number of deer that were shot with 45 and 50 cal my wife and kids took anumber that way and I climbed the ladder so to speak looking for something more effective, I did not stop at 54 I shoot a 58 and a 62 after using a 54 the rainbow trajectory did not appeal to me and the much slower ball did not stop them in there tracks like the 54. That 54 cal ball with 130 gr of RS and a 35 inch barrel is a real stopper. Lee