Effectiveness of hunting cartridges depend a lot on how an individual bullet behaves in game. At one time I analyzed several of the "killing power" formulas and they all seemed designed to prove the biases of their authors. Some favored initial bullet diameter, others bullet weight, some velocity and many favored sectional density of undeformed bullets. None that I have seen do a decent job of compensating for different bullet types.
For a long time, sectional density (weight divided by diameter squared) was considered by many to be one of the most pertinent measurements for medium and big game "killing power". It is still useful when working with non-expanding, non-fragmenting round and flat nosed bullets. What really happens inside game with other types of bullets, though, is that the the "effective SD" changes from expansion (increased effective diameter) or core (weight) loss. Bullets that maintain their weight (many bonded and monolithic) tend to penetrate much deeper with a lower initial SD than traditional cup and core bullets. Bullets that maintain a large expanded diameter may penetrate less than expected from "parachute effect".
Partition and similar bullets limit weight loss and maximum expansion by assuring that the base stays intact and cannot expand. Whole other classes of bullets depend upon full or partial fragmentation to damage tissue around the wound track. In short, most "killing power" formulas have very limited usefulness and are no longer viewed as being useful by bullet and ammo manufacturers except when limited to specific examples.
The most entertaining recent example is with the "Hornady Index of Terminal Standards" which was once very prominent on Hornady's website. The H.I.T.S. formula depends upon the weight of the bullet, squared, multiplied by velocity and divided by diameter, squared. It was developed around Hornady's cup and core bullets, but it turned out to be a terrible predictor for their own monolithic bullet performance in game. Copper alloy monolithic bullets are less dense and thus lighter weight than similarly shaped lead core bullets. The weight, squared component dramatically dropped their H.I.T.S score. Hornady's monolithic bullets retain virtually all their original weight, though, so their higher effective SD produces deeper penetration than Hornady's own expanding lead-core bullets, which typically lose some core weight. Although few seemed to notice, Hornady stopped using the H.I.T.S formula soon after it started producing its monolithic GMX bullets. I suspect it was largely because their own formula underestimated the real-world bullet performance of their own new bullets!
For a long time, sectional density (weight divided by diameter squared) was considered by many to be one of the most pertinent measurements for medium and big game "killing power". It is still useful when working with non-expanding, non-fragmenting round and flat nosed bullets. What really happens inside game with other types of bullets, though, is that the the "effective SD" changes from expansion (increased effective diameter) or core (weight) loss. Bullets that maintain their weight (many bonded and monolithic) tend to penetrate much deeper with a lower initial SD than traditional cup and core bullets. Bullets that maintain a large expanded diameter may penetrate less than expected from "parachute effect".
Partition and similar bullets limit weight loss and maximum expansion by assuring that the base stays intact and cannot expand. Whole other classes of bullets depend upon full or partial fragmentation to damage tissue around the wound track. In short, most "killing power" formulas have very limited usefulness and are no longer viewed as being useful by bullet and ammo manufacturers except when limited to specific examples.
The most entertaining recent example is with the "Hornady Index of Terminal Standards" which was once very prominent on Hornady's website. The H.I.T.S. formula depends upon the weight of the bullet, squared, multiplied by velocity and divided by diameter, squared. It was developed around Hornady's cup and core bullets, but it turned out to be a terrible predictor for their own monolithic bullet performance in game. Copper alloy monolithic bullets are less dense and thus lighter weight than similarly shaped lead core bullets. The weight, squared component dramatically dropped their H.I.T.S score. Hornady's monolithic bullets retain virtually all their original weight, though, so their higher effective SD produces deeper penetration than Hornady's own expanding lead-core bullets, which typically lose some core weight. Although few seemed to notice, Hornady stopped using the H.I.T.S formula soon after it started producing its monolithic GMX bullets. I suspect it was largely because their own formula underestimated the real-world bullet performance of their own new bullets!