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Sir Bob,

I gave up on lethality indices a long time ago, but you have rekindled the interest.
I never added the down range effects of BC for soft point loads, but lookout now, I got the itch!

Of course the Taylor KO has limits, and was only ever meant as a rough judge at efectiveness in knocking an elephant down
with a close miss of the brain on a head shot.
To me that means it should only be applied to solid bullets,
because that is the only type of bullet that should be shot into the skull of an elephant.
Also limited to the recommended DG rifles of the day, probably .366 to .622 caliber, from 9.3x62mm Mauser to .600 NE.
No needle-like flechettes at hyper velocity, nor manhole covers dropped on an elephant's head from a few inches above.

The TKO of a 50-pound, 25"-diameter manhole cover moving at 1 fps is huge ! TKO = 1250 exactly.
Compare to the 300-gr .375-cal at 2500 fps: TKO = 40 or 40.1 depending on how precise you need to be.
Or the 900-gr .622-cal at 1950 fps: TKO = 156.

OK, surely any lethality index has got to have limits on the projectile caliber it is applied to.

I am going to come up with one that may be arbitrarily applied to the bracket from .308-caliber to .458-caliber,
and bullet weights and muzzle velocities those calibers get routinely hunted with, using soft points.
We all know the .458 WinMag is more than big enough for any game animal that walks the planet,
and a .30-06 with the right bullet will do for the lower end of the spectrum of game weight.

Kinetic energy is not the answer. Much of it goes into noise and temporary wound channel and heating the meat.
Too much wasted sound and fury.
Momemtum is conserved in a more friendly-to-the-SWAG way.
Energy is conserved but kinetic energy evaporates into many other forms of energy.

Mass, caliber, velocity, and how they relate through sectional density and ballistic coefficient, that's the ticket
for my SWAG via KISS principle.

"Ballistic Product" (BP) is my new accounting method.
It is simply the product of 4 factors. Cute, eh ?

BP = (Bullet Weight in grains) x (bullet Velocity in fps) x (bullet caliber in inches) x (sectional density as based on pounds of bullet per square bullet CSA sq.in.)

BP = W x V x C x Sd

BP is numerologically cumbersome, too big, so it is converted to a unitless index by dividing it by 84,000.
That is arrived at by using 7000 grains per pound and 12 inches per foot: 7000 x 12 = 84,000

Ballistic Product Index = BPI = (BP / 84,000) = (W x V x C x Sd) / 84,000

Now we are cooking.

The final touch from Sir Bob's tutelage is to make it the "Terminal Ballistic Product Index" (TBPI)
by using impact velocity at locations downrange from the muzzle.
That's how BC gets involved.

But first I must start by calculating some TBPI at the muzzle velocity.

As Sir Bob said, we have to make our rough comparisons when using any index
by sticking with similar bullets by type of construction of the soft point bullet.
It is impossible to control for live game tissue impact due to its constantly changing state.
This is like horse shoes and hand grenades in many ways.