Question: "Muzzle Energy" vs. "Power Factor"

[butlers]

All,

I'm having trouble understanding what's more important -- "muzzle energy" (i.e. kinetic energy¹) vs. "power factor" (i.e. momentum²).

MUZZLE ENERGY

Most of the reading I've done focuses on energy as the determining factor in the lethality of a given caliber/round. Thus, the conventional wisdom is that you need a minimum of 1,000 foot-pounds of energy to kill a deer and 3,000 foot-pounds to kill a brown bear, etc. But since energy places a lot of emphasis on speed, you can come up with some pretty ridiculous examples.

Jellyfish: The stinger of a jellyfish is one of the fastest things in nature³. If you do the calculations, a 0.50 nanogram jellyfish stinger traveling at 45,000,000 meters/second = 0.0000000077 grains at 147,637,795.28 feet/second = 373.38 foot-pounds of energy

Bowling Ball: At the other end of the spectrum, you have world record holders who can throw a 15 pound bowling ball at 27 miles/hour⁴ = 105,000 grains at 39.60 feet/second = 365.53 foot-pounds of energy

Comparable "muzzle energy", but what would you rather have hurled at you? A microscopic needle or a 15 pound projectile? Now let's look at bullets.

9x19mm: 115 grain Winchester FMJ bullet traveling at 1,190 feet/second⁵ = 361.53 foot-pounds of energy

.45 ACP: 230 grain Winchester FMJ bullet traveling at 835 feet/second⁶ = 356.00 foot-pounds of energy

Again, similar muzzle energy, but which has the better reputation for "knock down"?

POWER FACTOR

If we switch from energy to momentum, the numbers above change drastically:

Jellyfish: The super fast but super light stinger has a power factor of 0.0011 kilo grain-feet/second (or 0.000023 Newton-seconds)

Bowling Ball: The super slow but super heavy bowling ball has a power factor of 4,158 kilo grain-feet/second (or 82.12 Newton-seconds)

Makes sense, right? A nanogram thrown at you -- even very very very fast -- ain't gonna do much to you, but a 15 pound bowling ball hurled at 27 miles/hour towards your face is going to hurt. And comparing bullets:

9x19mm: power factor of 136.85 kilo grain-feet/second (or 2.70 Newton-seconds)

.45 ACP: power factor of 192.05 kilo grain-feet/second (or 3.79 Newton-seconds)

Again, makes sense: .45 is perceived as having more stopping power than 9mm.

QUESTION

So is muzzle energy still the king?

If so, why is .308 Winchester (~2700 ft-lbs) considered inadequate for large predators (e.g. grizzly):
https://www.m4carbine.net/showthread...08-for-Grizzly

But .458 SOCOM (~2500 ft-lbs) is considered good to go?
https://www.m4carbine.net/showthread...g-Bear-Defense

Is it the greater power factor of .458 (600 kgr-ft/s) vs .308 (463 kgr-ft/s)? Or is it something else -- sectional density? Bullet weight and diameter? Expansion and penetration? What am I missing here?

Taylor has one answer:
https://en.wikipedia.org/wiki/Taylor_KO_Factor

Looking for additional insight from the experts here at m4carbine.net

Respectfully,
butlers


FOOTNOTES

1 Source:
https://en.wikipedia.org/wiki/Muzzle_energy

2 Source:
https://en.wikipedia.org/wiki/Power_...ooting_sports)

3 Sources:
https://www.sciencedaily.com/release...0508180735.htm
https://www.popsci.com/jellyfish-syringe-sting

4 Source:
https://www.bowlingdigital.com/bowl/node/14269

5 Source:
https://www.luckygunner.com/winchest...fmj-ammunition

6 Source:
https://www.luckygunner.com/winchest...0fmjwinusa-500