“Stopping Power” is a blanket term used to describe the energy imparted by a bullet. It combines the data points of bullet size, bullet weight, and bullet speed to predict how much damage the bullet will do if fired into the body of an attacker. Most often, this calculation is expressed in “foot-pounds” of energy- often (incorrectly) described as how many pounds of force are exerted against a square foot of bad guy body or other material.
EXAMPLE– in the gun store, you may hear someone declare:
“That little .380 doesn’t have enough stopping power!”
The design of modern self-defense projectiles mostly negates the differences in bullet weight and diameter. Also, “Stopping Power” formulas don’t take into account anything about the attacker, or their clothing, or if they are moving, or the angle of the bullet impact, or anything else.
Imagine I were to say that the “Triple-decker-four-cheese-bacon-butter cheeseburger” at my favorite restaurant is a healthier choice than the same burger with extra pickles. Because less sodium, you know. Stopping power reasoning is kinda like that.
Your ability to quickly and efficiently send multiple bullets into your attacker is far more important than how much “stopping power” one of those individual bullets is said to have.