Energy transfer is not what kills deer or you could shoot them in the @$$ and the "Hydrostatic Shock wave" so many speak of would kill them just as quickly as a shot in the vitals. Bullets that don't exit tend to kill a little quicker because they are typically softer highly frangible bullets that expand to a larger diameter and do more damage to the tissue they passed through.

A Remington 45-70 300gr bullet has a muzzle energy listing of 1810 fp.
A Remington 243 100gr bullet has a muzzle energy listing of 1945 fp.

According to the people who tout this energy transfer stuff the 243 clearly has more stopping power at close range. I doubt seriously that a 100gr 243 bullet would pass completely through a large Kodiak brown bear. So you are certain to dump all of that rounds energy into him. You are being charged by a Kodiak brown bear. Which gun do you want in your hands, the 243 or the inferior 45-70. LOL!

There is the world of paper ballistics and then there is the real world. Large holes in vital organs kill. Energy transfer is important in regards to your toaster browning a slice of bread. It doesn't have much to do with hunting.

VERY VERY moderate .45-70 load.

The Hornady LeveRevolution loads are running pretty conservatively, and in my 18.5" Marlin Guide Gun 1895, the 325grn FTX runs 1795fps.

That means a muzzle energy of 2325ft.lbs.

I push 90grn pills from a .243win to 3200fps, that's about 2045ft.lbs.

That's 15% more potential energy.

Now compare the increased bullet diameter component and the overall momentum value, i.e., the Taylor KO factor...

.45-70 .458", 325grns at 1795fps = 38

.243win .243" 90grns at 3200fps = 10

What's that mean? For equal penetration depth, the .45-70 will do about twice as much damage, for equal expansion, it will penetrate about twice as far (energy shed is an exponential function, 4x taylor equates to about 2x relative factor, i.e. 2^2).

So nice try, but you missed the boat...

I was always under the impression, you want the bullet to not exit the animal, ad more momentum will be used inside the body cavity making a cleaner kill. I never thought it was very accurate because, I've seen my dad hit deer with his .300 Weatherby Mag, and drop 'em where they stand, and I've seen people hit deer with smaller calibers where there's no exit wound and we've had to track deer for hours. I hunted with a 12GA for years, and I've only ever dropped 1 deer where she stood and I was aiming high and I had one pellet hit her right above the eye at 85 yards. And the bullets never came out the other side.

Try the 300 grain Federal factory loads. They are loaded with the 300 grain Speer hot cores. Dunno how many deer that I have flattened with them. No complaints. I have recovered one of them, and that was because I seen where it hit the hill on the other side of the deer. Shot one at 200 yards head on, and the bullet came out the other end. Am now loading 420 grain hardcast with a heavy charge of IMR 4198. Recoil is pretty stout, but if I run across a grizz in the hills with an attitude I know that I can stop it quick.