A 180gr solid and a 180gr frangible has the exact same "energy", yet are completely different in flesh.
"Energy" is not a wounding mechanism, never was and never will be. It is an idea that was dreamed up in a time when they didn't know how to measure "killing ability".
That time is long over. How bullets kill and why is COMPLETELY known. It is simple- placement of wound, depth of wound and width of wound. That's it. Full stop.
If the bullet in question has enough retained velocity when it impacts the target to expand/upset/fragment/whatever, then it will kill just fine.
As for the difference between external ballistics with the 308 and 6.5..... It is possible to get very close. We compete with a 308 load that is within pressure limits yet launches a 185gr Berger at 2,800fps from a 26in barrel MR2000. It does over 2,700fps from a 22in barrel.
Yet UNEQUIVOCALLY in the field we get less hits in the same guns than we do with 243's/6.5Creed/260Rem/etc. Why is that? I mean ballistically they are so close you can't really hold the difference in the field, right? Wrong. And it's one word- SHOOTABILITY. It absolutely can not be over stated. Especially in lighter weight hunting guns the differences in hit rates (group size in the field) from varying positions, on varying targets under stress is measurable. It is for every single person. Given the same platform and mechanical precision, there is no one that can shoot a gun with 25ft-lbs recoil as well as they can a gun with 15ft-lbs of recoil. That is a mechanical fact proven through thousands of shooters.
There is so much more to killing animals at medium-long range than just external ballistics. Recoil, muzzle lift, mental focus, follow through, muzzle blast, etc all contribute to pushing one to NOT do what is required to hit things. They less stable the position, the more wind, the more physically and mentally stressed one is, and the shorter time span one has- the more the differences show themselves.
If both bullets cause enough tissue damage, both drop and drift the same, both have the same mechanical precision, and both arrive with sufficient velocity to cause bullet upset- the one with less recoil and less muzzle rise, will ALWAYS result in more hitting and killing. It is only with drastic changes in terminal ballistics that you see an increase with going bigger.
An example would be a 300 magnum using a 178gr AMAX started above 3,000fps. There is a massive, measurable difference in wound channels between that a 168gr AMAX in a 308win going 2,700fps. Yet even then- the actual "killing ability" (that is how many shot fired for how many animals dying) almost always favors the lesssor recoiling platform. Some people can shoot well enough to do very, very well with the 300's, but the vast majority will have better success with a 6mm/6.5mm even though they have less "power".
