Q: It seems to me that hunters have been conditioned to judge a bullet’s terminal potential by the amount of energy it has left when it strikes the target.
As anyone who has used a 400 or 500gn lead bullet from a .45-70 in the field can testify, there’s a lot more to killing power than foot-pounds. This is especially true of a match bullet which rates the same amount of foot-pounds of energy as a controlled-expansion big-game bullet.
What’s your take on this?
Mick Moran
A: I agree with you. Not only weight but diameter and construction contribute to a bullet’s lethality.
Foot-pounds (or Joules or whatever you use) of energy is sometimes called “paper energy” because it is a mathematical number that in physics means, loosely, the capability to do work. The lethal effect or killing power of a bullet is closely associated with kinetic energy.
Ballistic tables give energy at the muzzle as well as at different ranges, but what really counts is the energy that can be delivered to the impact, because it has a direct effect on killing power. But the knockdown effect at impact is related to momentum.
Getting down to the nitty-gritty, knockdown is a matter of mass times velocity (momentum), not kinetic energy.
Penetration and expansion are both results of velocity and energy, and as the velocity slows down as the range increases, so does the bullet’s ability to penetrate.
Bullet weight can be helpful in this regard. The heavier bullet may arrive a bit slower, but still be more effective. If two bullets strike downrange with the same velocity, the heavier bullet will have more penetration and do more damage, all else being equal.
If two bullets are different in shape and materials, but hit with the same velocity and have the same mass, they will both impact with the same kinetic energy, but the damage inflicted on the game will differ depending on the bullet’s diameter, construction, degree of expansion etc.
One other critical factor: rotational speed imparted by the rifling does not decrease like velocity; it stays near constant throughout the bullet’s flight. Thus it too has an important effect upon bullet performance and the amount of tissue destroyed.
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