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Find The Boots

Rantings from a few corporate types about life, technology, travel, guns, politics, and everything good in the world.

What happens when you fire a gun into the air?

Thursday, May 10, 2007


The bullet eventually comes back to earth, but will it hurt someone? I've heard the myth that people can be killed by falling bullets. Every year around July 4th the police make statements in the paper warning people not to shoot in the air. My local version of Pravda, which also has printed the term "semi-automatic revolver", claims it can kill people.

Several years ago my roof developed a leak. I called out a roofer and he found the problem. The bill actually read "Removed bullet from roof." According to my measurements, it was a .223 round that someone had fired into the air. I live in the city, so it makes you wonder.

So let's try some of our own myth busting. TierFlyer isn't around to test on, so let's work a model. NASA has a cool calculator for computing terminal velocities. A bullet leaves with a high muzzle velocity, but that has little to do with the terminal velocity it will reach when it returns to earth other than how high it will start its fall back.

Let's use a 220-grain .30-06 round for our test. That's a moose load. In fact, it knocks them right down. I know this from personal experience.

The bullet is 7.62mm in diameter, so the cross sectional area is 45.6 mm (roughly 0.15 sq ft). The weight of that big 220 grain bullet is about 14g, or 0.03 lbs. I'll assume the drag co-efficient is 0.01 (it can't be zero) and it's a bullet, so it's aerodynamic. How high will it go? I have no idea, but let's assume 35,000 ft, about 6.5 miles. Going higher doesn't affect the calculations much.

For the moose load, we get a terminal velocity of 232.888 fps, imparting 35.27 joules on impact. How much is a Joule? Hint: at 3,000 fps it delivers 2,926.4 joules on impact. Big difference. Compare that to a paint ball marker which will fire 300 fps. Or getting hit by an 80-mph slap shot in hockey, about 104 Joules. The bullet would hurt, might injure, and would definitely leave a bruise, but I don't think this is going to kill someone. But it will put a hole in your roof.

Interestingly enough, if you try this with smaller weapons, you get higher terminal velocities. Do the math -- a 128gr 9mm round comes back down much faster than the moose load, but with less kinetic energy on impact. About half.

So are you going to kill someone by shooting into the air? That's a tough sell. But you could do property damage and you might injure someone. And as any long range shooter will tell you, the wind will carry those rounds a long way, so it's likely to land somewhere else than your house. Don't do it with anything larger than shot.

And wear glasses and a hat with a brim when you're out on the dove field, because as any bird hunter can tell you, sometimes it rains lead. But don't tell my local paper or the cops that bird hunters shoot into the air all the time.

   

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1 Comments:

  • At 1:46 PM, Blogger wyl247 said…

    NASA estimates the drag coefficient for bullets at .295

     

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