Talk of "wasted energy" is just that... wasted energy. Bullets, be they round ball or otherwise, don't kill by imparting energy...the energy is used by the bullet to punch holes through flesh and bone. If it didn't exit, it didn't have enough mass or energy to begin with, in my book. The idea that a bullet that stays in game rather than exiting somehow did more damage is false. If it had "more energy" it would have exited. If it expanded and seemingly did more damage, it was the wider hole, not a "dumping" of energy.
There is ALWAYS energy transfer when a bullet strikes a target that will slows or stops its travel.
A gallon of supermarket drinking water shot with a 50 caliber rb driven by 90 gr of FFF at 25 yards will illustrate this. But at 100 yards do to reduced velocity the jug will not be so violently effected.
Big animals are not water jugs and they are not solid water so their mass and the air in the lungs for example, reduce the shock wave effect that would be seen in a jug of water.
This is a 5+- gallon jug of water shot with my 16 bore rifle.
Its energy transfer that causes the jug to react as it does.
Having shot deer with this rifle at similar distance I can assure you that the effect is less violent and the deer not only may not fall down but likely will run off 20-50 yards before falling.
High levels of energy transfer require high velocity (like the 50 RB at 25 yards) and a large diameter or rapidly expanding bullet is needed to get really effect. Pushing a 1/2" rod into a gallon of water will not cause the jug to violently decompose. For the most part BP simply does not produce the velocity to make massive energy transfer (such a shooting a prairie dog with a modern varmint rifle) possible at hunting ranges. Shooting deer with HV bullets that are prone to rapid expansion can light weight for the energy they carry can cause significant meat loss for the hunter because of the rapid energy transfer causing wide spread bruising (blood shot) of edible parts.
To step into the brass suppository world a 243 win will transfer more energy to a target with the right bullet than a similar energy level 45-70-405 BP load will simply because the low velocity load will not cause massive disruption of the bullet as it encounters tissue. It will kill the animal well if placed right and produce no meat loss. But it will penetrate through a deer from almost any angle where as the modern HV bullet will loose its velocity much faster and is likely to stop in a relatively short distance compared to a 405 gr lead alloy bullet from a 45-70.
I should be building fence right now..... So I am shutting this off by saying that in the traditional ML world use a ball weight suitable for the game I like 50 cal for deer for example and consider is a nice safe minimum, use enough powder to get a trajectory and accuracy that is suitable and don't worry about energy levels. Its there, but in our world it does not mean much.
Dan