It is true that a bullet exitting takes some energy with it, the question is how much? If it exits at 100fps or 1000fps it makes a big difference. One is 600ft-ibs one is next to nothing.
There is of course no way of testing that on an animal, but there has to be a way to come up with some good geralizations.
Also run the same bullet, lets say a 215 berger, at 30-06 speed or 300rum speed. The 300 could exit the far side and still transfer more energy into the animal.
I honestly think we are making this issue more complicated than it needed to be for what it is worth, esp. when we do not have the means to measure it as you noted. The overall goal should be a load combination where the maximum energy dump (transfer) is absorbed by the animal at the point of impact. Personally, it does not matter to me what the velocity of the bullet or fragments that manages to exit. The video states 40-90% fo the bullet's mass disperses upon 3-5" penetration depending on impact velocity. That is a very substantial amount of energy dump. The majority of my Berger kills do not have exit wounds. So it is obvious that you also want to capitalize on the impact velocity, impact energy, bullet design performance at the point of impact, and of course shot placement.
The Berger design capability to dump maximum energy nearly upon impact and without the necessary pass-through to kill an animal is what made me switch from Nosler Partition and Accubond to Berger. It also reduces the risk of injuring/killing another animal behind target game esp. at long ranges unnecessarily - not visible during the target acquisition or whatever the case may be.
Since you are talking about 215 Berger. If I used my .300 WSM currently loaded with 215 Berger at 2800 FPS and if I adhere to my unwritten rule of 1000 FT-LBS of energy for deer and 1500 FT-LBS of energy for elk, my numbers are:
For elk: 950 yards, 1812 FPS, and
1568 FT-LBS
For deer: 1350 yards, 1461 FPS, and
1019 FT-LBS
However, because I want to keep the velocity threshold at a minimum of 1800 FPS, my self-imposed maximum range would be the same for both, 950 yards (even though the calculated energy for deer at 1350 yards meets the 1000 FT-LBS threshold). I like to keep things simple when possible and this is simply the guide I go by, instead of worrying about the wasted energy when the bullet manages to exit or at what velocity. This, in essence, is "my" generalization.
Cheers!
