The priority of using energy measurement as one factor in evaluating bullet terminal performance is helpful. However, because such mathematically calculated influence does not directly relate to terminal performance, it is a less persuasive metric.
Many other variables have as much influence or more. The characteristics of the bullet is first, and that includes weight, shape and design. Then there is velocity and deformation and penetration. When any one of these characteristics do not contribute to the dance adequately, terminal performance is compromised.
The best Bullets/caliber will have consistent terminal performance characteristics that meet set goals. The standard for such testing is the FBI gel tests. While not real world, the conditions are the best we have at the moment to compare disparate ideas on Bullets terminal performance. The FBI test does not claim to be real life—it is only a scientific method for approximating performance.
The matrix is:
1. Penetration between 12-18”, with the lower number considered better. Most non-expanding bullets can meet this standard in bare gel.
2. Expansion of the bullet to 1.5x the beginning diameter of the bullet. Ideally the bullet will continue to hold together to deliver the necessary penetration even after expansion. This is the bigger holes do more damage theory, as long as they are deep enough. Retaining weight after expansion usually results in better expanded penetration.
3. A Bullet that can break through objects on the outside of the body, such as clothing, and/or inside the body, such as bones sinew and muscle. Here is where ME probably comes into play, as obstacles can quickly reduce velocity/design shape and render bullet performance less adequate to continue penetration expanded with retained bullet shape going straight through to the desired depth.
4. The actual path of the bullet through a living target is unpredictable because of barriers and changes in density. It is possible to shoot a target multiple times with effective ammunition and not stop the target. Shot placement is a huge factor for success. The average shooter trained to defensively shoot Center of Mass (CoM) has a poor chance of stopping a fight quickly unless his bullet gets to the spine with sufficient velocity (FPE) to destroy it. Often CoM hits allow an aggressor to continue to fight for 30 seconds to a minute, a time frame within which most gunfights will end.
Because of all these other variables and requirements, FPE is only a factor in choosing a caliber/loading, and it’s a fairly low one. Again, it is a mathematical formula being applied to a real world experience arena that has many (more important) variables.
Prioritizing those variables is penetration, then expansion, then weight retention, then straight tracking to the intended target (spine or head). Velocity is one factor making up FPE, but it does not correlate directly to bullet performance given so many other variables. Mass is another factor, but it too is not an isolated dominant factor in terminal performance effectiveness, especially if it’s velocity is low.
In a mix of variables attempting to predict bullet terminal performance, FPE is there and always will be, but it is one of many somewhat lesser influencers in the caliber, bullet, cartridge load debate. Too many people have lost their lives by bullets that miss many of these parameters.
Priorities in choosing a caliber/load go deeper than just bullet terminal performance. The size, reliability, capacity, shootability, carry convenience, accuracy of the gun all contribute to being able to hit the target in the first place so the bullet can do its work.
The other metric for successful shoots terminating an attack is the number of rounds fired that strike the target effectively. The one shot stop with a defensive handgun is a rarity. Multiple shots hitting, 3-5, especially aimed toward spine or head, will do the job quickly, and may even do it with two substandard hits then one coup d’ grace.
FPE is not irrelevant, it is just not very determinative in selecting caliber/cartridge combos for killing felons because of so many other more important factors.
