IMO, cartridges should only really be ranked in groups when using various "killing power" formulas, with great difficulty in determining differences in actual killing effect between cartridges very close to each other in velocity/bullet weight/diameter, "knockdown", momentum, kinetic or other formulas. For example, I defy a fellow to tell me the difference in killing power {with proper bullets in each} on, say, deer, between a 6.5x55 and a .280 Remington. But compare the 6.5x55 and a .416 Rigby on buffalo, and you will see differences. Where do the differences FIRST manifest themselves?

THAT is the point best left to fireside arguments.

What JPK is saying can be demonstrated in test media where one bullet may penetrate identically with another, but the one may produce significantly different radial energy transfer to the media. And this can occur between cartridges that develop the same velocity and use the same bullet weight, the difference being only the bullet shape. Thus the difficulty in using a mathematical formula only in estimating "killing power".

Comparing in test media can demonstrate this.

This is why I take with a grain of salt many assertions of killing power promoted by certain handgun aficionados. Many revolver bullets will outpenetrate high velocity rifle loads, but the effect on the test media {and game} may be dramatically different. Just because a bullet punches deep holes doesn't mean it will kill as well as another round that doesn't penetrate as deeply but may transfer the energy of its bullet to the target in the form of massive trauma.

There are circumstances, obviously, where deep penetration is the most important goal of a bullet, though to be sure.

And energy cannot be totally tossed out, depending on game to be shot. There are circumstances where energy may be a roughly better estimator of killing power, such as when light game is shot. A 500 grain RN shot at 1700 fps striking the ribs of a small deer may leave you with a long day of tracking, whereas the same critter shot in the same place with a fast .25 cal bullet may put you in venison without much looking.

I am no mathematician, but I am curious. Thus I have been fascinated to compare various cartridges in my test media, and pistol bullets in butcher sheep. Unfortunately I've never tested the big NE or elephant rounds in any media...