KNOCKDOWN POWER

9mm ammo

A lot of people take umbrage with the term “knockdown power, because it conjures the idea that a bullet will take a man off his feet, like being hit by a car. It won’t. Action movies are wrong. Nevertheless, knockdown power can be an important measure of a cartridge is capable of. What people really mean by knockdown power is how hard does a given round hit. If we pretend that shot placement, bullet type, wound channel, penetration and target distance aren’t factors (which they definitely are), the amount of force a bullet delivers onto its target would determine its potency. Fortunately, that force is easy to measure.

How do you measure the amount of energy a bullet can deliver downrange? Foot-pounds. A foot-pound (FT-LB) is a unit of energy equal to that required to raise 1 pound a distance of 1 foot. So, knockdown power, by my definition, is a consistent, repeatable and standard way of measuring how powerful a round is.

  • Foot-Pound = (Mass x Velocity²) / 450,435
  • Knock Down Power = (Bullet Grain x Feet per Second²) / 450,435
  • Example: 124 Grain bullet, traveling 1,126 FPS  (124 X 1,126²) / 450,435 = 349 FT-LBS
  • Example: 115 Grain bullet traveling 1,250 FPS  (115 X 1,250²) / 450,435 = 399 FT-LBS

In the above example, the round with the heavier bullet is not the more powerful round, as many would have assumed. This is the general idea behind the 9×19 round’s effectiveness. It offers an excellent balance of weight and speed, with many variations to fine tune things to your liking.

Lets compare FT-LBS of the 9mm to that of the legendary .45 ACP.

  • 9mm:           115 Gr @ 1,250 FPS = 399 FT-LBS
  • .45 ACP:       230 Gr @ 845 FPS    = 365 FT-LBS
9mm ammo

All you .45 lovers, don’t get your panties in a bunch. The .45 is a hell of a round that has proven itself effective, time and time again for over a hundred years. It’s shown its capabilities in multiple wars and is still a benchmark in handgun ammunition today. Also, I admit that there are a lot more factors to being a “man stopper” than FT-LBS. For instance; a properly expanded .45 hollow point will leave a 3/4″ permanent cavity in soft tissue and that’s just the start. All I’m pointing out is that the supersonic 9mm luger round offers more energy (FT-LBS) than the subsonic .45 ACP. It’s science.