Hacker News Reader

Comment by sobriquet9 | Hacker News Reader

Per https://mythresults.com/episode50, Mythbusters found that if a bullet is fired upward at a non-vertical angle, it will maintain its spin and will reach a high enough speed to be lethal on impact. Because of this potentiality, firing a gun into the air is illegal in most states, and is not recommended by the police in the others. Also the MythBusters were able to identify two people who had been injured by falling bullets, one of them fatally injured.

The non-lethal was only if the bullet was fired perfectly straight up using precision alignment. It seems to be a common disinformation tactic to take this section out of context and claim that Mythbusters said shooting up was fine.

I don't see a contradiction between what I said and what Mythbusters have found [1].

> In the case of a bullet fired at sufficiently close to a vertical angle to result in a nonballistic trajectory, the bullet would tumble, lose its spin, and fall at a much slower speed due to terminal velocity, so is rendered less than lethal on impact (the Busted rating). However, if a bullet is fired at a lower angle allowing for a ballistic trajectory (a far more likely case), it will maintain its spin and will retain enough energy to be lethal on impact (the Plausible rating). Because of this potentiality, firing a gun into the air is illegal in most U.S. states, and even in the states where it is legal, it is not recommended by the police. Also, the MythBusters were able to identify two people who had been injured by falling bullets (fired from about 1 mi (1.6 km) away, hence at a lower angle), one of them fatally (the Confirmed rating). This is the only myth to receive all three ratings at the same time.

[1] https://en.wikipedia.org/wiki/MythBusters_(2006_season)#Epis...

You said "Terminal velocity of bullets fired above approximately 60 degrees is not high enough to be lethal." Mythbusters found that any angle more than a few degrees off of straight up (i.e., below 87 degrees) was enough to establish a ballistic trajectory and be lethal.

There is a huge difference in difficulty between 30 degrees, which is easy enough to eyeball, and 3 degrees which requires careful aiming with a specialized tool.

Let's take a common 9 mm round with muzzle velocity of 1,100 fps. When fired at 87 degrees, horizontal velocity component is 1,100 fps * cos 87 deg = 57 fps.

It will be much less than that on the way down due to air resistance throughout the flight, and negligible compared to terminal velocity (around 200 fps).

Per https://en.wikipedia.org/wiki/Celebratory_gunfire, a bullet traveling at 200 feet per second can penetrate human skin. So even terminal velocity is significant and can injure or kill.

The reason perfectly vertical bullets are less dangerous is that they tumble and this tumbling reduces the terminal velocity below dangerous levels. Presumably tumbling could also happen at lower angles due to wind or other factors, it just is less likely.

It takes considerably more to kill someone than to break the skin. Maybe if you are laying on your back and the falling bullet hits the carotid artery, but this is a really contrived example.

Wow thank you for this. Literally almost believed him. The amount of authority people speak with is just insane. Literally the truth was the exact opposite.

Goes to show people believe the thing that's most convenient for them to believe.

See my other comment. Mythbusters found the same thing, that bullets fired at low elevation remain dangerous, while bullets fired at high elevation (close to vertical) come down at a much lower velocity, not sufficient to kill a person.

Thank you, I remembered vaguely that episode but couldn't find a reference to it.

Related, this Forbes articles explains the matter and links to a few documented cases:

https://www.forbes.com/sites/startswithabang/2020/07/02/the-...

This appears to be a poorly-sourced "research" page put together by a marketing agency. There's really nothing there about the methodology of this work, and there's plenty to suggests the authors have very little knowledge of firearms (a fired bullet in the first animation is shown with a casing, there's no discussion of bullet aerodynamics which are going to be very different for most sharp-tipped rifle bullets and for handgun rounds, etc) or physics (e.g., no accounting for energy when evaluating the velocity at which a bullet can penetrate skull).

Ya, their predicted descent velocity/lethality is not right. Most ammunition will destabilize and begin to tumble long before it reaches its peak as it transitions from supersonic to subsonic.

My guess would be the dangerous situation here is intoxicated people shooting up in the air but then also in other directions in a careless inebriated state.

Okay, but what if you were on the Moon? Would the absence of atmospheric friction result in a different outcome? Also, I've heard you could fire a bullet on the Moon and it would be able to go into as low an orbit as a few 100 meters without ever hitting the ground. What's the minimal velocity for that to be plausible?

> Would the absence of atmospheric friction result in a different outcome?

Yes.

> Also, I've heard you could fire a bullet on the Moon and it would be able to go into as low an orbit as a few 100 meters without ever hitting the ground. What's the minimal velocity for that to be plausible?

Apparently: 1679 m/s per https://www.quora.com/How-fast-must-an-object-be-moving-to-o... . The answer isn't very sensitive to height because the radius in the equation is from the center of the moon, so the answer will only change a tiny amount.

Note that low orbits on the Moon aren't stable. The Moon's gravity is lumpy due to its composition, so things that are low quickly become unstable and crash.

> What's the minimal velocity for that to be plausible?

The escape velocity, which is 2.4 km/s on the surface of the moon, so you would need a pretty powerful gun :p

Low lunar orbit is a bit less than that, ~1.7 km/s. Higher than a rifle round, but a "kinetic energy penetrator" from a tank gun gets that fast [0]

Many years ago I read a short story about a gun battle on the moon where the bullets orbit the moon. Took me an hour to find it:

Men of Good Will by Ben Bova & Myron R. Lewis

Galaxy v22n05 (June 1964), p 170. [1]

0. https://en.wikipedia.org/wiki/Muzzle_velocity

1. https://archive.org/details/Galaxy_v22n05_1964-06_modified/p...

Actually experimental results show that the bullet will kill at almost every angle.

Source? In the case Mythbusters mentioned, the person killed by falling bullet was about a mile away, hence those bullets were fired at a lower angle.

Fun story about mythbusters, there's a reason they never claimed to be rigorously scientific. Because they weren't.

They tested a couple different firearms, and basically could not find the impact in the ground from larger calibers (because high altitude wind took it away) and so just dropped some bullets from a low altitude balloon and assumed terminal velocity was the only thing in play, and openly admitted this limitation.

They occasionally joked that "the only difference between playing around and science is writing it down" on the show but openly talked in interviews about how mythbusters SHOULD NOT BE TREATED AS SCIENCE and should instead drive interest in science

Let's do science then.

Terminal velocity of a falling 9 mm bullet is 219 fps, .223 bullet falls at 244 fps. [1]

To perforate the skin and enter the underlying subcutaneous tissue and muscle, a minimum velocity in the order of 230 fps is necessary. [2]

So the bullet falling at terminal velocity has barely enough velocity to break the skin, and is therefore very unlikely to be fatal.

[1] https://forensicmcq.com/terminal-velocity-of-falling-bullets... [2] https://pubmed.ncbi.nlm.nih.gov/7304523/

It's actually in the "Conclusions" section of your source.

"Can" kill, surely. The article contrasts hitting a child in the temple versus grazing an adult in the leg.

Reply on news.ycombinator.com