Again, I turned to a basic physics text that explained that momentum is mass in motion. Momentum is the mass of an object times the velocity of the object. In this instance, less emphasis is placed on velocity than with the kinetic energy formula and more emphasis is placed on mass. Mass and velocity are given equal weight.

Hard-cast bullets with blunt tips penetrate well and transfer energy.

While the 165-grain bullet from the .30-06 has 2.6 times the kinetic energy of the .44 Magnum load, it has only 1.3 times the momentum. Either kinetic energy or momentum can be used to describe the "power" of a projectile, and both have a sound basis in physics. What has never been quantified exactly, however, is killing power or killing ability.

Answers Are In Actual Shooting
Here, we find that practical field examples from shooting game or empirical evidence from shooting into an expansion medium is the best test. Over the next few seasons my hunting partners and I shot several head of elk and deer with the muzzleloader. What we learned was that the 370-grain T/C Maxi slug would put an elk down quickly and probably more reliably than most centerfire .30-caliber rifles. We also learned that while the heavyweight .50-caliber Maxi slug is deadly on elk, a lightweight .50-caliber round ball is not. In fact, the round ball was not particularly impressive even on deer.

I also have learned through the years that handgun bullets of .400 diameter or larger work great on deer and boar. I have taken several deer, wild boar, and other game with the 10mm Auto. Here, a 200-grain bullet at nearly 1200 fps has proven mighty effective. If a bluntnosed hard-cast semiwadcutter bullet is used, it almost does not matter whether the bullet expands. It is still effective with reasonably placed shots.

As in any hunting situation, shot placement is important. A poorly placed shot will not put an elk down with authority, whether it's from a .375 H&H Magnum rifle or a .44 Magnum handgun. A traditional handgun is a limited-range firearm, but other types of handguns, such as the break-action single-shot Thompson/Center Encore and bolt-action Savage Striker, are chambered for bottleneck rifle cartridges and when used in conjunction with scopes these firearms are as accurate as a rifle. For purposes of this discussion, however, I'm talking about traditional semiautomatic and revolver rounds. With revolvers and semiautomatics we generally get close to game before shooting, and we tend to place our shots better.

A rifle bullet going fast carries a lot of kinetic energy. If a high-velocity rifle bullet expands well, it transmits a high level of energy to game shortly after impact. Someone termed this "hydrostatic shock." The bullet also tends to destroy itself. Frontal diameter gets large and then smaller again as such a bullet penetrates, and expanded petals fold back along the bullet's shank. Lead at the front end of the bullet smears off under the high-velocity impact and the bullet loses weight. The large frontal diameter and loss of weight combine to reduce penetration. The greater the expansion, shock transmission, and weight loss, the less the penetration.

Kinetic energy is a measure of destructive potential, and it applies equally to both high-velocity rifle bullets and slow-moving handgun bullets. But projectiles with equal kinetic energy do not necessarily have equal killing power. After a high-velocity rifle bullet impacts, there are lots of variables related specifically to bullet performance. How it expands and transfers energy becomes very complex and dynamic. A high-velocity expanding bullet is constantly changing along its path through game. All sorts of bullet construction innovations have been employed to maintain bullet integrity under high-velocity impact. Manufacturers have gotten very good at it in recent years.