How does one determine the power of a gun? What's the difference between a .45 and a 9mm, .22, .357 etc?

Question

How does one determine the power of a gun? What's the difference between a .45 and a 9mm, .22, .357 etc?

Answer 1

The "power of a gun" I am asuming you mean the power applied to the target. Terminal ballistics is an inexact science, but from a physics standpoint, you simply multiply the velocity times the mass and you have the force being applied to the target.

The Calibre is the diameter of the bullet, this is combined with the specifications of the cartridge shell to determine the final outcome of the power to be applied.  A . 45 caliber could be a shotgun, a handgun, or a rifle, however a 45 ACP is a handgun round.

A 9mm could be a 9mm Parabellum, a 9mm Largo, a 9mm Makarov...

Just using the number reference is not the full story.

Marie

Answer 2

Calibers are usually the width of the bullet.

How many grains the round itself weighs and how many grains of powder there are to propel the round must be factored in.

Answer 3

Diameters of the bullet are in inches

.22 inches

.357 inches

.45 inches

.357 inches is the same as 9.07 mm.

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The energy of a bullet is a function of the weight of the bullet, the diameter, the gun barrel length which results in a change in the speed.