Choosing Home Defense Gun? Understand Terminal Ballistics

If you are evaluating a firearm for self-defense use, you should consider three main factors: Reliability, Functionality (sights, trigger, ergonomics), and Effectiveness (ability to halt/neutralize threats). Regarding effectiveness, you need to consider what happens when the projectiles from your firearm reach the target. That involves penetration and terminal ballistics.

A 12ga shotgun is very effective inside 20 yards, with less risk of over-penetration* vs. a centerfire rifle.

You’ve probably heard the term “Terminal Ballistics”. But do you really know what this refers to? Fundamentally, “Terminal Ballistics” describes the behavior of a projectile as it strikes, enters, and penetrates a target. Terminal Ballistics, then, can be said to describe projectile behavior in a target including the transfer of kinetic energy. Contrast this with “External Ballistics” which, generally speaking, describes and predicts how projectiles travel in flight. One way to look at this is that External Ballistics covers bullet behavior before impact, while terminal ballistics covers bullet behavior after impact.

The study of Terminal Ballistics is important for hunters, because it can predict how pellets, bullets, and slugs can perform on game. This NRA Firearm Science video illustrates Terminal Ballistics basics, defining key terms such as Impact Crater, Temporary Cavity, and Primary Cavity.

External Ballistics, also called “exterior ballistics”, is the part of ballistics that deals with the behavior of a non-powered projectile in flight.

Terminal Ballistics, a sub-field of ballistics, is the study of the behavior and effects of a projectile when it hits its target.

*This Shooting Illustrated article discusses over-penetration risks with a variety of cartridge types. “A bullet passing through a threat and continuing with the potential to cause unintentional damage to a bystander or object is a situation commonly described as over-penetration.”