Knockdown Power

[JohnKSa]

The .40 S&W is the most commonly used caliber in Law Enforcement these days followed by the 9mm and the .45ACP.  All of these calibers churn out muzzle energy numbers in the 350-450ftlb range with typical self-defense loadings.  Bullet weights range from about a quarter ounce to around half an ounce.

Should be plenty of knockdown power, right?

Mythbusters did a test with a .50 BMG rifle at essentially point-blank range.  For those of you who don't have the "personal statistics" of the big 50 memorized, it uses a bullet that weighs between 1.5 and 1.75 ounces and pushes it out the muzzle at around 2800fps.  Muzzle energy? 

A massive 13,000 ftlbs.

Impressive, right?  Now THAT's knockdown power!  Except it's not. 

The Mythbusters specially prepared a dummy for this test.  An armor plate was welded into the chest to be sure to stop the bullet fully inside the dummy.  They wanted to make sure that the dummy absorbed ALL the energy the bullet was carrying.  Then the dummy was carefully balanced on a set of iron rails so that it could be easily dislodged by the force of a thrown baseball.  The dummy weighed about 160lbs.

Then they shot it from a few feet away with a .50 BMG rifle.

Here are some captured video frames**.

Note that the rod through the dummy's chest can easily slide off the rails.  And yet in the last frame the dummy has fallen mostly straight down after the impact bumped the rod off the rails.

In the side view it's clear that the dummy moves backward only a few inches as it falls downward out of the frame.


Think your favorite handgun caliber has knockdown power?  Don't kid yourself!

But don't feel too badly--neither does a .50 BMG rifle...

** (The frames are NOT consecutive frames nor are the intervals between the frames similar, the frames are chosen to show the dummy's movement during the test.)

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So then is the 9mm a better bet?

[JohnKSa]

No matter what you choose, if it's something you can carry on you, it won't "knock" someone down.  They may fall down abruptly if you severely damage their central nervous system or if they have a psychologicial predisposition to fall down when shot, but they won't be "knocked" down.

The point is that any time you are tempted to spend agonizing over caliber selection or specific loadings in a particular caliber is FAR better spent practicing.  Dryfiring, doing presentations, practicing drawing from cover, actual range work, etc. will build skills that will make much more difference in the outcome of a self-defense shooting than the caliber you've chosen.

I am NOT saying that caliber makes no difference.  Especially when you start getting to the extremes, there are differences in performance.  If you're comparing a .25ACP to a .45ACP, there are terminal performance issues that are pertinent.  But comparing calibers commonly accepted as being suitable for self-defense/law enforcement work is largely a waste of time.  If it will penetrate adequately with expanding ammunition and as long as it doesn't hamper your ability to shoot accurately and rapidly it's a good choice.