These are always interesting conversations. Many with theories have no mathematical background to back up opinions. However that stops nobody from having an opinion!
Muzzle Energy is a measure of energy, but not fully applicable to a bullets performance on tissue. So those using it as a reference are factually handicapped in the discussion. It was a SAAMI design to compare cartridges against each other, not on the tissue of game animals.
A rifle that has 3000 FPE cannot move 3000lbs. It's simply a formula that puts the priority of the result in velocity, not the weight of the projectile. Velocity is squared in the formula not weight. Velocity squared times bullet weight divided by 450240
Momentum is Mass times velocity, As an example:
180 grain bullet ( mass), times 3000fps ( velocity) = 540,000 divided by 7000 (7000grains in a pound) = 77.1lbs of momentum or impact force.
That means that the bullet would actually move anything lighter then 77.1 pounds upon impact. It's why 3000FPE cannot move a deer, or any living big game from impact. No shoulder fired arm can shoot a projectile that will lift a big game animal off it's feet. Those who claim so have seen an animal jump at impact but they have not seen a big game animal thrown from impact.
So that this math riddle is cleared up for the basics. What does matter speed or diameter? Really depends upon the species. I've never seen a Cape Buffalo, rhino, hippo, elephant, bison, wild cattle, Giraffe, impressed with velocity. They do however show a significant respect for bullet weight and diameter.
Two different things cannot occupy the same place at the same time. This is what causes so much trauma when very high velocity impacts something small or fragile. When the High Velocity bullet impacts a coyote for example. The tissue moves out of the path at nearly the speed of the projectile. The cavity will stress the surrounding tissue as it's compressed against the outer hide. Many times this hide will rupture and leave you with the exploded coyote or other small creature. As body mass increases the hide can contain the rapidly expanding tissue and hold it together. This compresses the tissue into a huge hematoma. Or what folks refer to as blood shot meat.
On very large animals, the tissue or muscle density can contain this rapid expansion to the local region and reduce the trauma to only a small area. It's why the bigger species do not realize the same trauma from High Velocity as the smaller Species do. Its about body mass. Hence the reason for large heavy projectiles in Africa back in the day. It was recognised that deep penetration was the ticket to success. Those 500 grain and 700 grain bullets would drive deep into and often out of anything in it's path.
Using the momentum formula for my 458 Lott
500 x 2350= 1175000 (divided by 7000 grains in a pound) 167 pounds of momentum on the surface of a .458 diameter bullet. You can probably envision the amount of penetration this would have.
Now there is very good news here in all of this. The decision for HV or heavy weight is coming to a very good compromise with todays monolithic projectiles. Penetration can be achieved with lighter bullets that retain all their weight and still expand.
in the late 50's when the 300 win mag was introduced it was to be the king of all hunting cartridges on earth! Every single writer, outfitter, guide, and Professional hunter was very impressed and believed this cartridge to be the apex of ballistics engineering for the big game hunter.
The cartridge could shoot a 180 bullet at 3100fps. This was a massive lethal combination. But lets think about this. Upon impact the bullet would go to pieces. The cup and core technology was not in step with the case capacity that provided the extreme velocity. How could any manufacturer produce a different bullet when the same one needed to be used in the 30/06 with a much lower speed. With 1000's of 30/06 rifles to every new 300 win mag, nobody was going to make their bullets just for the 300 win mag speeds! Nosler Partitions were made which helped quite a bit, but even so they still lost half the weight/ mass and were better, but not good enough to make use of the 3100fps speeds.
Today, a 30/06 with modern rifles, modern powders and the monolithic bullets, like the TSX far exceed the lethal performance of the 300 Winchester Magnum of the 60's.
The 30/06 today shooting a 165 grain bullet at 2950 on paper is not better. However in practice this bullet retains all its weight upon impact. So thinking back to the momentum calculation which will penetrate better?
165 grains or the crumbled mass of the cup and core bullet which may be at 90 grains after impact if it's lucky? More likely there would be many pieces in the 25-40 grain weight
I guess the real answer to this question is not whether faster or heavier is best. But rather which retains it's weight better when the projectile comes to rest.