# Bullet Speed
**URL:** https://boards.straightdope.com/t/bullet-speed/516285
**Category:** Cecil's Columns/Staff Reports
**Created:** [November 4, 2009, 3:36pm UTC](https://boards.straightdope.com/t/bullet-speed/516285 "2009-11-04T15:36:03Z")
**Posts on this page:** 18
**Page:** 1
### Author:  [@Wheelz](https://boards.straightdope.com/u/Wheelz)
#### Post date: [November 4, 2009, 3:36pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/1 "2009-11-04T15:36:03Z")
Re: [How does a bullet or knife kill somebody? - The Straight Dope](http://www.straightdope.com/columns/read/186/how-does-a-bullet-or-knife-kill-somebody)
Cecil said:
> [@Cecil Adams](#):
>
> Speed (muzzle velocity) is the most important factor; we learn from physics that kinetic energy, i.e., destructive power, increases arithmetically with mass, but geometrically with velocity.
I don’t doubt Cecil is correct, but I need my own ignorance fought regarding the physics. One of the very few things I remember from High School Physics class is:
_F=ma_
This would seem to suggest an arithmetic relationship to both speed and size.
What don’t I know?
---
### Author:  [@Telemark](https://boards.straightdope.com/u/Telemark)
#### Post date: [November 4, 2009, 4:10pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/2 "2009-11-04T16:10:17Z")
KE = 1/2 (M \* (V \* V))
Kinetic energy = 1/2 Mass x Velocity^2
I believe this is the relevant formula. So, increase your speed and the KE increases geometrically.
F=ma involves force and acceleration, not KE and speed.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [November 4, 2009, 4:43pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/3 "2009-11-04T16:43:49Z")
Just to nitpick, that’s a quadratic dependence on speed, not geometric.
**Wheelz** , while F = ma is probably the single most important thing to retain from a physics class, the fact that force and energy are different is right up there with it.
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### Author:  [@Telemark](https://boards.straightdope.com/u/Telemark)
#### Post date: [November 4, 2009, 5:03pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/4 "2009-11-04T17:03:50Z")
> [@Chronos](#):
>
> Just to nitpick, that’s a quadratic dependence on speed, not geometric.
I went into computers so I could stop taking math and physics classes. 🙂
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### Author:  [@hogarth](https://boards.straightdope.com/u/hogarth)
#### Post date: [November 4, 2009, 5:24pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/5 "2009-11-04T17:24:36Z")
> [@Wheelz](#):
>
> Re: [How does a bullet or knife kill somebody? - The Straight Dope](http://www.straightdope.com/columns/read/186/how-does-a-bullet-or-knife-kill-somebody)
>
> Cecil said:
> I don’t doubt Cecil is correct, but I need my own ignorance fought regarding the physics. One of the very few things I remember from High School Physics class is:
>
> _F=ma_
>
> This would seem to suggest an arithmetic relationship to both speed and size.
> What don’t I know?
“a” (= acceleration) is not the same thing as speed. It’s the change in speed over time.
---
### Author:  [@Bad\_Astronaut](https://boards.straightdope.com/u/Bad_Astronaut)
#### Post date: [November 4, 2009, 6:29pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/6 "2009-11-04T18:29:35Z")
[QUOTE=The Master]
Large bullets, and small bullets that travel very fast, such as those from an M-16 rifle, can kill almost instantly, mainly by reducing the region of impact literally to hamburger. They also generate something known as “hydrostatic shock.” The body is composed largely of water and as such may be viewed as a hydraulic system. Liquid being noncompressible, the shock caused by the high-velocity entry of a large projectile (don’t you love this technobabble?) is transmitted throughout the body, causing widespread organ damage and disruption of nervous functions. Even a wound to an arm or leg can be fatal in some instances.
[/QUOTE]
Is it bad that I find this totally awesome?
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### Author:  [@signal11](https://boards.straightdope.com/u/signal11)
#### Post date: [November 5, 2009, 1:14am UTC](https://boards.straightdope.com/t/bullet-speed/516285/7 "2009-11-05T01:14:18Z")
> [@Bad\_Astronaut](#):
>
> Is it bad that I find this totally awesome?
No, but you have no idea the bee’s nest you’re stirring up. As far as internet flame wars goes, this one’s a doozie.
Terminal ballistics are extremely contentious area of study. I’m surprised that no one has come in with the “hydrostatic shock is a myth” yet.
I predict that this thread will not die for some time.
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### Author:  [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)
#### Post date: [November 5, 2009, 2:48am UTC](https://boards.straightdope.com/t/bullet-speed/516285/8 "2009-11-05T02:48:38Z")
> [@hogarth](#):
>
> “a” (= acceleration) is not the same thing as speed. It’s the change in speed over time.
Actually, it’s the change in velocity over time. Acceleration, like velocity, is a vector. Speed is a scalar.
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### Author:  [@Martini\_Enfield](https://boards.straightdope.com/u/Martini_Enfield)
#### Post date: [November 5, 2009, 12:16pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/9 "2009-11-05T12:16:57Z")
> [@signal11](#):
>
> No, but you have no idea the bee’s nest you’re stirring up. As far as internet flame wars goes, this one’s a doozie.
>
> Terminal ballistics are extremely contentious area of study. I’m surprised that no one has come in with the “hydrostatic shock is a myth” yet.
I was going to say, there is no way that a 5.56mm FMJ round (which is what an M-16 fires) is capable of blowing someone’es arm off.
In fact, I believe one of the major criticisms of the M-16 (and the SA-80, and the Steyr etc) is the lack of “stopping power” of the 5.56mm round compared to the 7.62x51mm NATO round it replaced.
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### Author:  [@SeanArenas](https://boards.straightdope.com/u/SeanArenas)
#### Post date: [November 5, 2009, 4:31pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/10 "2009-11-05T16:31:38Z")
> [@Martini\_Enfield](#):
>
> I believe one of the major criticisms of the M-16 (and the SA-80, and the Steyr etc) is the lack of “stopping power” of the 5.56mm round compared to the 7.62x51mm NATO round it replaced.
I had a friend in the military who said they used to try to get their hands on the older gun because it was more powerful than the newer one!
---
### Author:  [@running\_coach](https://boards.straightdope.com/u/running_coach)
#### Post date: [November 5, 2009, 4:43pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/11 "2009-11-05T16:43:33Z")
> [@Martini\_Enfield](#):
>
> **I was going to say, there is no way that a 5.56mm FMJ round (which is what an M-16 fires) is capable of blowing someone’es arm off.**
>
> In fact, I believe one of the major criticisms of the M-16 (and the SA-80, and the Steyr etc) is the lack of “stopping power” of the 5.56mm round compared to the 7.62x51mm NATO round it replaced.
Working from memory and it may not be true but I understood the original M-16’s twist rate was too slow and did not stabilize the bullet, resulting in yawing/tumbling when it struck the target.
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### Author:  [@Martini\_Enfield](https://boards.straightdope.com/u/Martini_Enfield)
#### Post date: [November 6, 2009, 1:40am UTC](https://boards.straightdope.com/t/bullet-speed/516285/12 "2009-11-06T01:40:19Z")
> [@runner pat](#):
>
> Working from memory and it may not be true but I understood the original M-16’s twist rate was too slow and did not stabilize the bullet, resulting in yawing/tumbling when it struck the target.
I’m pretty sure that’s been debunked. I know the .303 Mk VII cartridge would “tumble” on impact because it was designed to do so (the 1929 _Textbook of Small Arms_ published by the British government mentions that the bullet has an aluminium core-tip), but that’s because of the bullet’s design and not the rifling in the gun.
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### Author:  [@Patch](https://boards.straightdope.com/u/Patch)
#### Post date: [November 6, 2009, 1:53am UTC](https://boards.straightdope.com/t/bullet-speed/516285/13 "2009-11-06T01:53:27Z")
> [@runner pat](#):
>
> Working from memory and it may not be true but I understood the original M-16’s twist rate was too slow and did not stabilize the bullet, resulting in yawing/tumbling when it struck the target.
Any bullet where the center of pressure is in front of the center of gravity will tumble after entering a dense medium, like tissue. If you look through Dr Martin Fackler’s research you can find .22LRs that tumble. (And tumble is an incorrect description - the bullet will rotate 180 degrees and finish traveling base first.)
The current 5.56 bullet fired by the M-16 series will rotate after 3-4 inches of travel. I suspect the earlier bullet with the 1 in 14 twist went through it’s yaw cycle earlier, like the 5.45x39 fired by the AK-74.
---
### Author:  [@md2000](https://boards.straightdope.com/u/md2000)
#### Post date: [November 9, 2009, 5:16pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/14 "2009-11-09T17:16:06Z")
F=ma
Therefore F=The force required to accelerate the bullet to muzzle velocity from rest.
(Also the force impacted on the target, to take the bullet from impact velocity to zero.)
The difference is speed change due to air friction in flight.
KE=(1/2) mv^2
So yes, if you hit with twice the mass of bullet, you double the energy.
If you hit with twice the velocity, you impart 4 times the energy.
Make that 3 times the mass, 3 times the energy; 3 times the velocity, 9 times the energy. Etc.
However, energy cannot be created or destroyed - so to get twice the velocity you need 4 times as much enegy in the explosive cartridge. 3 times = 9 times the explosive, etc.
And of course, the faster the bullet the greater the air resistance, so now aerodymanics and range come into play. A relevant stat I once heard for aircraft; to get a plane going twice as fast, it needs eight times the horsepower; air resistance is a cube ratio. Plus you get into secondary effects - shape of the bullet affects air resistance, length of barrel determines whether all that extra explosive actually does its job, or is most of the oomph wasted once the bullet has already left the barrel. Some of the energy is converted into radial motion as the bullet spins, etc.
You can argue armchair physics all day, but nothing beats actual experimental data.
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### Author:  [@signal11](https://boards.straightdope.com/u/signal11)
#### Post date: [November 9, 2009, 7:10pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/15 "2009-11-09T19:10:31Z")
> [@SeanArenas](#):
>
> I had a friend in the military who said they used to try to get their hands on the older gun because it was more powerful than the newer one!
There are really only two cases of a small handful of people preferring an older service weapon over a more recent iteration, that of the M-14 and the M1911.
Both had to do with the caliber of the weapon and not the weapon itself.
There might have been a difference between what he said and what you understood because I was an infantryman and the instances I would have preferred an M-14 or a 7.62mm weapon over an M-4/5.56mm.
Outside of certain specialized roles, the modern soldier is much more effective with an M-16/M-4 than he would be with an M-14.
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### Author:  [@Martini\_Enfield](https://boards.straightdope.com/u/Martini_Enfield)
#### Post date: [November 10, 2009, 4:57am UTC](https://boards.straightdope.com/t/bullet-speed/516285/16 "2009-11-10T04:57:26Z")
> [@signal11](#):
>
> There are really only two cases of a small handful of people preferring an older service weapon over a more recent iteration, that of the M-14 and the M1911.
I’ve heard several Australian/NZ/British soldiers express a preference for the L1A1 SLR over the Steyr (or the SA80), both as a gun and for the cartridge it fires.
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### Author:  [@Mr.Krebbs](https://boards.straightdope.com/u/Mr.Krebbs)
#### Post date: [November 11, 2009, 3:29pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/17 "2009-11-11T15:29:32Z")
> [@Martini\_Enfield](#):
>
> I’ve heard several Australian/NZ/British soldiers express a preference for the L1A1 SLR over the Steyr (or the SA80), both as a gun and for the cartridge it fires.
Brits preferring the FAL to the SA80 makes sense due to the latter weapon’s (dismal) reputation. I have never heard anything that wasn’t positive from Aussies issued the AUG. Although I can grasp a preference for 7.62 - I personally have three “evil” 7.62 firearms but only one 5.56 - excepting southpaws, what reasons do the combat arms guys give for not liking the AUG? Nostalgia?
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### Author:  [@Martini\_Enfield](https://boards.straightdope.com/u/Martini_Enfield)
#### Post date: [November 11, 2009, 10:38pm UTC](https://boards.straightdope.com/t/bullet-speed/516285/18 "2009-11-11T22:38:57Z")
> [@Mr.Krebbs](#):
>
> Brits preferring the FAL to the SA80 makes sense due to the latter weapon’s (dismal) reputation. I have never heard anything that wasn’t positive from Aussies issued the AUG. Although I can grasp a preference for 7.62 - I personally have three “evil” 7.62 firearms but only one 5.56 - excepting southpaws, what reasons do the combat arms guys give for not liking the AUG? Nostalgia?
Lack of stopping power and range, getting smacked in the eye by the scope if you hold it wrong, and the fact large parts of it are made of plastic. It’s not a _bad_ gun, but everyone I know who has used the SLR prefers it to the Steyr.