Death from above

From time to time we find bullets in cars. Usually, they’re fired into the car. (I know. Welcome to the Bay Area.) This time the bullet had clearly fallen from the sky, since it was mostly undamaged.

If you’re one of the people who shoot in their backyard on the 4th (or any other time), we can’t be friends. You’re irresponsible. I’m not anti-gun, but I am anti-dumbass.

As we were gawking at the bullet, I began to wonder how dangerous a bullet fired into the air would be. What if I was unlucky enough to be standing in the wrong place at the wrong time. Would it break the skin? Crack my scull? Will a falling bullet kill you?

I’m No Physicist

I’m not the kind of guy who can throw a bunch of calculations up on a whiteboard from memory. (Actually, let’s imagine one of those clear chalkboards. That way the camera can catch my look of concentration as I scribble Greek letters.) However, I figured I could find an online calculator easily enough.

Let’s see. I’ll need the weight of the bullet (124 grain, ~8 grams). Its speed should be 216 ft/second (65 m/sec). And if we assume it lands nose first, we can pretend it’s a 9mm sphere.

Well, apparently, I’m not smart enough to find / use a calculator to find the answer I was looking for, so I switched approaches. I decided to go with something I know, power factor.

Power Factor of a Falling Bullet

I like shooting sports and I also like reloading. In action shooting ammunition can be loaded as Major or Minor. Major is a power factor (PF) of 165 or up. Minor is 125 PF or up. What is power factor? Power factor is the bullet’s weight times its velocity divided by 1000. What does it mean? It’s the amount of damage a round will do to its target. A power factor of 125 is lethal. It’s common for police and military rounds like 9mm parabellum. Why use a round with a power factor of 165? Well, it’s even more lethal-er. (‘murica)

So, what’s the power factor of a low-power round like the .22 long rifle? Usually about 65. It’s not considered a defensive round, but I certainly wouldn’t want to be shot with one.

How about our falling bullet? It’s a 124 grain 9mm bullet, so we have the weight. Terminal velocity is 216 ft/second, so we have its speed.

124 x 216 is 26,784

26,784 / 1000 = 26.74. Let’s round that to a power factor of 27. Well, that’s a whole lot better than the 125 PF in front of the muzzle, but is it safe?

Is a bullet with a power factor of 27 dangerous?

Let’s compare our falling bullet to the paintballs people shoot each other with for fun. They sting, and as your mom probably warned, “You’ll put your eye out with that thing!” A 49-grain paintball traveling at 290 ft/second has a power factor of 14. Our falling bullet has twice the wallop. What’s that mean? I don’t really know other that I’d rather be shot with a paintball than a falling 9mm round.

Human Testing

For testing I built a 9mm air rifle that would fire rounds at 216 ft/sec and rounded up a few friends to help with testing. In order to be scientific, I included friends with different body types and some with light clothing and others with thick jackets.

Just kidding. No people were harmed in my quest for knowledge.


A small digression. I was talking to a guy at a brewery, and he said, “I miss the days when we couldn’t find out.” I asked what he meant, and he said back in the good old days that whenever a question would come up in conversation, people would discuss, guess, and theorize, but in the end, nobody knew for sure. Now someone looks it up on a phone and everybody knows the answer instantly; it’s not as much fun. And he has a point.

What’s the internet say about falling bullets?

Will the falling bullet break the skin? Yes. Will it crack my scull? Yes. I’ve included links to the NIH and CDC below.

Sure, I’ll probably survive, but I’m enjoying life without any injuries caused by some moron shooting a gun in the air. I’ll end this post the way I started it. Don’t shoot your gun in the air. For that matter, don’t do anything irresponsible with your gun. Keep your guns secured. Always point your gun in a safe direction. Don’t shoot your gun anywhere that you’re not allowed to fire a weapon.

NIH opinion piece

CDC study of celebrator gun fire in Puerto Rico

Additional reading