Bullet Drop (of a different kind)

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Bullet Drop (of a different kind)

Post by Die Judicii » 12 Mar 2018, 8:41 pm

Hi all,
I've been in Limbo for a while and will kick off with a query that needs some opinions/answers/ballistic expertise.

Q: Theoretically speaking, if a small calibre such as .17 HMR was fired at a bird high up in a tree,,, and missed, would the projectile after running out of velocity and propulsion have the ability to be dangerous as it free falls back to ground given its small physical size and only weighing the 17 grains ?
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Re: Bullet Drop (of a different kind)

Post by Gwion » 12 Mar 2018, 8:57 pm

Dunno. Not volunteering as a test subject, though! :D
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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 12 Mar 2018, 9:19 pm

No. Ever been to a duck opening. When I used to go you often get lead shot rain. I'm still here.

I also recall (I hope correctly) someone did the numbers and the story went that they would not do great harm except maybe very heavy bullets.
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Re: Bullet Drop (of a different kind)

Post by andreweden » 12 Mar 2018, 9:29 pm

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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 12 Mar 2018, 9:41 pm

Yeah, that's it, terminal velocity is not that high. But heavier bullets at a given velocity have greater energy and there for more dangerous. The small stuff like. 22 & smaller are unlikely to do a lot of damage. A 180gr would be a problem.
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Re: Bullet Drop (of a different kind)

Post by Thom318 » 12 Mar 2018, 11:02 pm

I can't rember the actual equation, but after reaching the peak of its arc, an object will accelerate towards earth at a rate of 9.8 meters per second, per second, before reaching terminal velocity.
The terminal velocity of the average 80kg human being skydiver is roughly 200km/h.
I can't remember the rest but Mythbusters reckon it was near impossible that a falling bullet is capable of breaking skin. :D
Still, I wouldn't want to get hit in the head with a falling bullet, I think it'd smart a bit
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Re: Bullet Drop (of a different kind)

Post by AusTac » 13 Mar 2018, 5:29 am

I have heard rumours of people dying over in the middle east after coping a falling projectile in the head from celebratory gunfire, but that's a 7.62×39 which is a fair bit heavier than a 17 hmr, would need a great big property before i was happy to pot shot birds with a rimfire though, mostly just because i'm a crap shot :lol:
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Re: Bullet Drop (of a different kind)

Post by on_one_wheel » 13 Mar 2018, 6:00 am

Terminal velocity calculation that I found on the net for interest.
"Use the terminal velocity formula, v = the square root of ((2*m*g)/(ρ*A*C)).
m = mass of the falling object.
g = the acceleration due to gravity. ...
ρ = the density of the fluid or gas the object is falling through.
A = the projected area of the object. ...
C = the drag coefficient."

I'm willing to bet that once it goes into free fall it might spin end for end slowing it down even more.

Also .... Mythbusters did a great episode on exactly that. It's definitely worth watching.

Cool topic :thumbsup:
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Re: Bullet Drop (of a different kind)

Post by on_one_wheel » 13 Mar 2018, 7:08 am

I can't find a video of Mythbusters episode 50 "Bullets fired up" but heres a list of the results from the episode.
https://mythresults.com/episode50
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Re: Bullet Drop (of a different kind)

Post by sungazer » 13 Mar 2018, 7:55 am

Ive read a study that was done. It is in Hatchers Notebook part 2 section 20 called Bullets from the Sky.
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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 13 Mar 2018, 7:57 am

Please explain.jpeg
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Very interesting result from myth buster's. But I would still say the smaller the lower energy.
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Re: Bullet Drop (of a different kind)

Post by sungazer » 13 Mar 2018, 8:08 am

Sorry OB before I had the brain in gear new I had seen it somewhere brain just had to reindex.
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Re: Bullet Drop (of a different kind)

Post by Gaznazdiak » 13 Mar 2018, 9:03 am

I remember a very convincing demonstration of area fire by an M60 mounted on a C2 Sight at Singleton in the 70's.
Using map coordinates they slaughtered an acre of innocent balloons from the other side of a large hill.
Can't remember the max effective range for the 60 used this way but my aging memory suggests it was 8 miles.
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Re: Bullet Drop (of a different kind)

Post by sungazer » 13 Mar 2018, 9:06 am

OB you are correct it is all about the weight of the projectile. They all fall at the same speed it is the weight that determines the energy that is imparted on hitting the ground / head , building ect.
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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 13 Mar 2018, 9:33 am

Yep, terminal velocity does vary depending on shape and mass, but it looks like a bullet from a 3006 will fall at 90m/s.

https://en.m.wikipedia.org/wiki/Terminal_velocity

From that site.
The biologist J. B. S. Haldane wrote,

To the mouse and any smaller animal [gravity] presents practically no dangers. You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object.
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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 13 Mar 2018, 10:13 am

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Re: Bullet Drop (of a different kind)

Post by Die Judicii » 13 Mar 2018, 5:29 pm

Oldbloke wrote: the resistance presented to movement by the air is proportional to the surface of the moving object.


So what yer sayin is,,,,,, If a woman were to fall off a skyscraper,, and spread her legs,,, she'd slow down before hitting the pavement ?
:lol:

Feel free to add your thoughts Brett,,,,,,,,,

Thanks for all the input fellas. :thumbsup:
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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 13 Mar 2018, 6:18 pm

Die Judicii wrote:
Oldbloke wrote: the resistance presented to movement by the air is proportional to the surface of the moving object.


So what yer sayin is,,,,,, If a woman were to fall off a skyscraper,, and spread her legs,,, she'd slow down before hitting the pavement ?
:lol:

Thanks for all the input fellas. :thumbsup:


DJ, Great to see you back on deck. And as they say, laughter is the best medicine. :lol:
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Re: Bullet Drop (of a different kind)

Post by Archie » 13 Mar 2018, 7:49 pm

sungazer wrote:OB you are correct it is all about the weight of the projectile. They all fall at the same speed it is the weight that determines the energy that is imparted on hitting the ground / head , building ect.


I am being a bit nitpicky here, and I could be wrong, but... not every projectile falls at the same speed (and I’m not talking because of different drag coefficients). Every projectile, ignoring drag and reaching terminal velocity, falls at the same speed only if it starts falling from the same height - because the constant is the rate of acceleration at 9.8m/s

The reason I mention it is because, I do not know but I would guess, if you shoot a 30-06 straight up into the air I’m betting it goes a lot higher than a .22. So when it reaches the top of its arc, it has more time to accelerate because it’s falling a longer distance. Which would mean it’s also going faster when it hits the dirt (or your head) - although I’m guessing it would probably reach its terminal velocity and stop accelerating before then.
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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 13 Mar 2018, 8:29 pm

"although I’m guessing it would probably reach its terminal velocity and stop accelerating before then."

I think that's close to the mark. But both the heavy 30-06 projectile and the lighter 22 projectile would have a slightly different terminal velocity too.
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Re: Bullet Drop (of a different kind)

Post by sungazer » 13 Mar 2018, 9:31 pm

Terminal velocity is reached from falling at not such high height a human body spread eagle is said to reach it falling from only 1500 ft. So pretty much all bullets will reach it on the way down. There is very little difference in the terminal velocity of objects due to size unless you go to the feather and ball sinker extremes. a marble and a cannon ball would fall at almost if not the same speed. The cannon ball would impart more energy when it stops due to its mass.
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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 14 Mar 2018, 12:25 am

Whikipedea says about 300fps.
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Re: Bullet Drop (of a different kind)

Post by Daddybang » 14 Mar 2018, 7:10 am

Oldbloke wrote:Yeah, that's it, terminal velocity is not that high. But heavier bullets at a given velocity have greater energy and there for more dangerous. The small stuff like. 22 & smaller are unlikely to do a lot of damage. A 180gr would be a problem.


Yep think about hail..a small pea size piece will sting a golf.ball size piece can kill. :thumbsup: :drinks:
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Re: Bullet Drop (of a different kind)

Post by sungazer » 14 Mar 2018, 7:21 am

What I meant OB was it doesnt take much of a rifle to shoot a bullet up 1500 ft in the air. If you can do this it will achieve terminal velocity on the way down and all of them will be pretty much the same speed (300fps) give or take on their drag.
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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 14 Mar 2018, 8:23 am

"Yep think about hail..a small pea size piece will sting a golf.ball size piece can kill. :thumbsup: :drinks:"

That's it.
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Re: Bullet Drop (of a different kind)

Post by Archie » 14 Mar 2018, 8:26 am

sungazer wrote:What I meant OB was it doesnt take much of a rifle to shoot a bullet up 1500 ft in the air. If you can do this it will achieve terminal velocity on the way down and all of them will be pretty much the same speed (300fps) give or take on their drag.


Ah right. Yep fair point, I misunderstood.

All the maths aside though - I've had birdshot land on my hat and it was more weird than anything, but I have zero desire to have that experience repeated with 7.62x39 at a wedding in Nowhereistan. Even if it should be fine... nah.
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Re: Bullet Drop (of a different kind)

Post by sungazer » 14 Mar 2018, 8:38 am

i doubt you would notice the difference between a 7.62*39 and a 7.62*51 :lol:
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Re: Bullet Drop (of a different kind)

Post by Oldbloke » 14 Mar 2018, 9:20 am

"I've had birdshot land on my hat and it was more weird than anything"

Happens all the time duck opening. Not a problem.
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Re: Bullet Drop (of a different kind)

Post by Hangfire » 14 Mar 2018, 12:01 pm

Gaznazdiak wrote:I remember a very convincing demonstration of area fire by an M60 mounted on a C2 Sight at Singleton in the 70's.
Using map coordinates they slaughtered an acre of innocent balloons from the other side of a large hill.
Can't remember the max effective range for the 60 used this way but my aging memory suggests it was 8 miles.


Only around 2 to 2.5 from memory of my support course 12 years ago and the bellets are coming like rain at that range beaten zone is only 50 odd meters long less even i think. Thats 7.62 in a mag 58. M60 is just less relaible version. The DFSW also use 50 cal mgs now and 40mm auto grenage launchers
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