It really depends on the size of the ball you are using, and the game you are shooting. Beer have very thin, soft bones, and even a .45 cal. RB will shatter them, and still penetrate to the lungs.
If you are hunting Elk, Moose, Mule Deer, And Caribou, or any Bear or Wild Boar, you need a lot more MASS, and preferably a bullet, to break the bones, and still penetrate well. The bones in these game animals are much more massive, and strong to break, compared to the Whitetail deer.
Whenever you are shooting a RB, understand its limitations as well as its assets. RBs expand rapidly in soft flesh, as well as when they hit solid bone. They are usually larger in diameter than most "deer rifle Cartridges" used in modern guns, so that the hole going into the deer is much larger than most "Deer Cartridge bullets" can expand to after striking the deer. But, a RB doesn't have a great Ballistics Coefficient, which means that it loses velocity very quickly.
If you want Shock to work for you, the RB has to be at least .58 caliber, or larger. Otherwise, a .54 BULLET will stop just about any of the larger game animals with authority.
A .50 caliber bullet will work well with the deer family game, but would not be my choice for hunting bear or wild boar. Bullets, even cast from soft lead, rarely expand unless they strike bone in these animals.
I would have the same comment about using a bullet of lesser caliber- fine for deer and for deer family game, but not something one would choose to shoot bears or wild boar. Now, where its legal, there are people who shoot deer in the head with .32 cal. bullet guns, and any bullet to the brain will result in instant death.