#1  
Old 04-30-2016, 06:41 AM
Mr. Bill Mr. Bill is offline
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Bullet-Proof Vests

It's a common, almost mandatory, trope in movies and TV. The hero is involved in a gunfight, takes one or more gunshots to the chest and goes down like a sack of beans. Later, after the dust clears, he peels back his shirt to reveal a bulletproof vest with the bullets lodged in the fabric of the vest, sometimes flattened, sometimes protruding out like there was no damage done to the bullet.

My question is, is this the way it actually happens? Does the bullet get lodged in the vest, or does it actually get stopped and fall away? With the absence of penetration, is the momentum of the bullet enough to knock someone down, with loss of voluntary muscle function for a moment or two?

On a related note, why is it that a kevlar vest will stop bullets, but not a knife?
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  #2  
Old 04-30-2016, 07:19 AM
Sasquatch Sasquatch is offline
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bullet proof (resistant) vests

That actually is the way most soft body armor works, especially for handgun bullets which tend to be larger diameter and slower. The bullet will be deformed by the impact, which actually helps spread the force and slow it down. It might just drop away, if it doesn't penetrate at all. If it hits harder, or the jacket tears and makes sharp edges, it might penetrate some of the layers of Kevlar and get stuck in the material.

Higher velocity rifle bullets (which are usually also smaller diameter) need hard plates to stop the bullet, usually fragmenting it; Army body armor plates will stop rifle armor piercing rounds even.

The momentum of a bullet impact is going to be less than the momentum from the recoil of firing it, so from a purely physics standpoint, no. However, people getting shot are not as prepared for it as people shooting. They may be off balance, and there is certainly some mental/physiological reaction to "I've been shot!" So falling down is not that unusual, especially if the person is just standing around. Someone in motion, or doing large movements, tend to keep on their inertial path.

Kevlar is still just a fabric, although tough. Getting poked with a finger and getting poked with a hatpin is pretty different, despite maybe being the same overall force. A sharp knife edge concentrates force on a tiny area, whereas a bullet impact is pretty much a really hard finger poke.
  #3  
Old 04-30-2016, 07:34 AM
AK84 AK84 is offline
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I have an old school friend who has been hit by a 7.62 x 39mm round while wearing a vest, with the plate.. A broken rib, a REALLY bad bruise and week of light duties.

I doubt that most circumstances would result in a person just getting up, probably have been, but I don't think Doc Brown would have been as alright as he was, if this was real life.

(Actually he took a burts at something like 5 meters, I wonder if any vest would stop all those rounds.).

Last edited by AK84; 04-30-2016 at 07:35 AM.
  #4  
Old 04-30-2016, 11:17 AM
Snarky_Kong Snarky_Kong is offline
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Quote:
Originally Posted by AK84 View Post
I have an old school friend who has been hit by a 7.62 x 39mm round while wearing a vest, with the plate.. A broken rib, a REALLY bad bruise and week of light duties.

I doubt that most circumstances would result in a person just getting up, probably have been, but I don't think Doc Brown would have been as alright as he was, if this was real life.

(Actually he took a burts at something like 5 meters, I wonder if any vest would stop all those rounds.).
I believe that the plates that US troops wear are rated for 3 hits.
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Old 04-30-2016, 11:43 AM
Raguleader Raguleader is offline
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What they tell us in the Air Force is that the plate will definitely stop the first bullet. After that, you should probably take the hint and seek cover.

EDIT: To clarify, military ballistic vests tend to be a soft vest with internal pockets that you can put solid armor plates in, typically made from some type of ceramic material I think. You can switch out for heavier or lighter plates, or go without them entirely to make the vest lighter (but less protective; it'll stop pistol rounds and fragmentation, but you better hope some bad dude isn't sighting you in with a rifle).

Last edited by Raguleader; 04-30-2016 at 11:45 AM.
  #6  
Old 04-30-2016, 04:26 PM
albino_manatee albino_manatee is offline
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here's what could become the future' new kid on the block … cfm's :

http://www.popsci.com/metal-foam-sto...s-than-an-inch

https://uk.news.yahoo.com/metal-foam...IEc2xrA3J1cmw-

Last edited by albino_manatee; 04-30-2016 at 04:27 PM.
  #7  
Old 04-30-2016, 06:48 PM
Ranger Jeff Ranger Jeff is offline
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Some of the more conscientious Huey crew chiefs would leave flak jackets on the benches for we grunts to sit on on the ride in.
  #8  
Old 04-30-2016, 06:55 PM
Chronos Chronos is online now
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Actually, you should probably take the hint and seek cover even before the first hit. The vest just provides a little extra insurance if you can't get to cover fast enough.
  #9  
Old 04-30-2016, 07:29 PM
Stranger On A Train Stranger On A Train is offline
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Joe Enema doesn't aways give you a radio check before he elects to sling some lead in your direction. That being said, armor has failed to protect a thundering herd of good troop, is always too hot, and pinches where it'll do the most pain regardless of how you pad and adjust it.

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  #10  
Old 04-30-2016, 08:04 PM
jasg jasg is offline
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Quote:
Originally Posted by Stranger On A Train View Post
Joe Enema doesn't aways give you a radio check before he elects to sling some lead in your direction. That being said, armor has failed to protect a thundering herd of good troop, is always too hot, and pinches where it'll do the most pain regardless of how you pad and adjust it.

Stranger
Is this a real life example of autocorrect being Our Greatest Enema?
  #11  
Old 04-30-2016, 08:06 PM
Bear_Nenno Bear_Nenno is offline
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Quote:
Originally Posted by Mr. Bill View Post
It's a common, almost mandatory, trope in movies and TV. The hero is involved in a gunfight, takes one or more gunshots to the chest and goes down like a sack of beans. Later, after the dust clears, he peels back his shirt to reveal a bulletproof vest with the bullets lodged in the fabric of the vest, sometimes flattened, sometimes protruding out like there was no damage done to the bullet.

My question is, is this the way it actually happens? Does the bullet get lodged in the vest, or does it actually get stopped and fall away? With the absence of penetration, is the momentum of the bullet enough to knock someone down, with loss of voluntary muscle function for a moment or two?

On a related note, why is it that a kevlar vest will stop bullets, but not a knife?
The bullets get caught in the vest. Here is a decent video showing bullets hitting kevlar. https://www.youtube.com/watch?v=kgBzqzSLdlY
What is not mentioned in the video is that a vest must not allow the hole in the clay to be deeper than 40mm, or the vest is not rated for that particular bullet at that velocity. In the test shown in the video, you can see how a vest can still stop bullets that it is not rated to stop, but the deformation in the clay will be great, which means that the person wearing it would have suffered greater blunt trauma. But at least it isn't a penetrating injury.
So it's possible for someone to be knocked down by a bullet while wearing a vest. It's also possible to just stand there and take it. It all depends on the vest and, of course, the rounds fired.
  #12  
Old 04-30-2016, 08:37 PM
Stranger On A Train Stranger On A Train is offline
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Quote:
Originally Posted by jasg View Post
Is this a real life example of autocorrect being Our Greatest Enema?
The misspelling was intentional.

I can attest to a ballistic vest not preventing you from getting some seriously painful contusions in the impact zone. The bullet may not penetrate, but it still hits like Joe Louis on speed.

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  #13  
Old 05-01-2016, 01:41 AM
pkbites pkbites is offline
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Originally Posted by Bear_Nenno View Post
The bullets get caught in the vest. Here is a decent video showing bullets hitting kevlar. https://www.youtube.com/watch?v=kgBzqzSLdlY
Yeah, but that was hit with rounds from a handgun.

Without a metal or ceramic plate rifle rounds will go through a vest like it's not even there!

Even with the plates only so many rifle rounds will be stopped. Which is why I was hyper critical of the scene* when Doc was saved by a vest that obviously took 20+ rounds. Even with a plate or flack jacket does he survive that.









*Heh. The new "Goodwins Law". Everything, eventually, goes Back to the Future!

Last edited by pkbites; 05-01-2016 at 01:42 AM.
  #14  
Old 05-01-2016, 03:13 AM
Bear_Nenno Bear_Nenno is offline
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Originally Posted by pkbites View Post
Yeah, but that was hit with rounds from a handgun.
I didn't think we were talking about rifles. I thought he meant things that are actually stopped by the vest, in which case they become embedded in the layers of material. Rounds that penetrate will... well, they'll penetrate. They'll go right on through. If plates are used, then whether or not the rounds become embedded depend on the type of plates and the specific round and velocity. If we're talking about ceramic boride plates used by the military, then the rounds will get embedded in the plates themselves. Old school steel plates, not so much.

As for the scene in Back to the Future: I always just figured Doc used a design that he invented himself. He can make a train fly; I'm sure he could figure out how to make a cool vest that stops anything.
  #15  
Old 05-01-2016, 03:26 AM
Ranger Jeff Ranger Jeff is offline
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Even if a vest stops the bullet from breaking the skin, there's still going to be some blunt force trauma. Yes, a broken or cracked rib or sternum can be painful, but considering the potential damage if they hadn't worn a vest, not too many guys are going to complain all that much.
  #16  
Old 05-01-2016, 03:48 AM
Bear_Nenno Bear_Nenno is offline
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Quote:
Originally Posted by Ranger Jeff View Post
Even if a vest stops the bullet from breaking the skin, there's still going to be some blunt force trauma. Yes, a broken or cracked rib or sternum can be painful, but considering the potential damage if they hadn't worn a vest, not too many guys are going to complain all that much.
If the stopped bullet is within the NIJ rating of the vest, then the blunt trauma will be minimal. The impact cannot cause more than 44mm (I incorrectly said 40mm earlier, but I just looked it up to be sure) of deformation in the clay behind the armor during certification testing. There is going to be some blunt force with any soft armor, but not at the level of broken ribs, provided of course that the armor was rated for the round. With hard armor, the blunt force trauma is almost nothing. Again, provided the plates are rated for the round. With the right plates, you can stand there and take multiple rounds like this guy:
https://www.youtube.com/watch?v=hdqaM-zpOQ0
  #17  
Old 05-01-2016, 04:16 PM
Hail Ants Hail Ants is offline
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This is why you should refrain from calling them 'bullet-proof vests', but instead refer to them as 'body armor'. Similar to how so-called 'lie-detectors' are better referred to as 'polygraphs'. Both are not even close to being 100% reliable.
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Old 05-01-2016, 10:01 PM
Siam Sam Siam Sam is offline
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Who needs body armor? Various cultures in Southeast Asia have magical tattoos, amulets and other charms that will stop bullets. I recall one guy in Cambodia, a candidate for a Darwin Award if ever there was one, inviting his friend to test his new bullet-stopping charm by shooting him at point-blank range.

Last edited by Siam Sam; 05-01-2016 at 10:01 PM.
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Old 05-02-2016, 07:16 AM
Martini Enfield Martini Enfield is offline
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The Zulu had something similar, I believe, and certainly spent part of the mid-late 19th century labouring under the misapprehension that cowhide shields could stop British rifle cartridges.

Spoiler alert: No, they can't.

Last edited by Martini Enfield; 05-02-2016 at 07:16 AM.
  #20  
Old 05-02-2016, 11:17 AM
lost4life lost4life is online now
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Obligatory Archer link.
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Old 05-02-2016, 02:15 PM
skdo23 skdo23 is offline
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How realistic was Emily Blunt's character's reaction to being shot while wearing body armor at about 8:53 in this video? Sorry, I couldn't find a shorter clip containing this scene.
  #22  
Old 05-02-2016, 02:43 PM
Chihuahua Chihuahua is offline
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Quote:
Originally Posted by skdo23 View Post
How realistic was Emily Blunt's character's reaction to being shot while wearing body armor at about 8:53 in this video? Sorry, I couldn't find a shorter clip containing this scene.
I don't know that there is a single "right" reaction to being shot. It depends heavily on the thickness of the armor, the caliber, and the muzzle velocity of the projectile.
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Old 05-02-2016, 02:44 PM
Enright3 Enright3 is offline
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Quote:
Originally Posted by skdo23 View Post
How realistic was Emily Blunt's character's reaction to being shot while wearing body armor at about 8:53 in this video? Sorry, I couldn't find a shorter clip containing this scene.
Just an FYI, you can add the start time on a YouTube link... ?t=8m53s
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Old 05-02-2016, 05:01 PM
Gray Ghost Gray Ghost is offline
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Have we done yet, the Second Chance guy shooting people with .308 while wearing his company's vests? (I'm wondering just what besides kevlar is in that vest.) IIRC, in the 70s and early 80s, Richard Davis, the CEO of what was Second Chance body armor, while trying to sell police departments on the idea of body armor, used to shoot himself with the policeman's own service weapon. No broken ribs. And it doesn't look like the shootee in the video above suffered any kind of injury like that. OTOH, I have read accounts of LEOs getting shot in their vest, and suffering bruising/broken ribs. YMMV depending on your vest and just how you get shot, I guess.

Anyway, as sasquatch wrote in post #2 of this thread, provided you're expecting the blow, pretty much all small arms bullets aren't going to knock you over from just the momentum of the bullet. What knocks you over is your reaction to getting shot or if you're otherwise off balance.
  #25  
Old 05-02-2016, 07:42 PM
Isilder Isilder is offline
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The rifle bullet might go through a vest .. While it might reduce the velocity the trade off is that the vest may have helped reshape the bullet , flaring it out to do MORE injury even when lesser speed. The vest might help reduce injury from a snipers steel jacket bullet, as it will reduce speed but not deform.

(the sniper needs to go through glass and similar and still have the bullet travel straight. Depends on his choice of bullet at the time.. He might know he has no glass in the way... )
  #26  
Old 05-03-2016, 12:09 AM
Bear_Nenno Bear_Nenno is offline
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(I'm wondering just what besides kevlar is in that vest.)
In 1984? It's most likely steel trauma plate inserts.
  #27  
Old 05-03-2016, 07:41 AM
Raguleader Raguleader is offline
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As an aside, I remember in one of the Police Story movies, Jackie Chan is trying to talk down a hostage taker with a gun, and the confrontation ends with the hostage taker taking a shot at Jackie before being subdued.

Naturally, Jackie rips open his jacket to reveal a bullet proof vest! Followed by one of the other cops saying that it was a good thing Jackie was wearing two vests because that shot would have killed him at that range otherwise. Cue Jackie removing the vest to reveal another vest layered under it.
  #28  
Old 05-03-2016, 09:05 AM
Boyo Jim Boyo Jim is offline
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Originally Posted by Ranger Jeff View Post
Even if a vest stops the bullet from breaking the skin, there's still going to be some blunt force trauma. Yes, a broken or cracked rib or sternum can be painful, but considering the potential damage if they hadn't worn a vest, not too many guys are going to complain all that much.
On the contrary, I'd complain a LOT more because I'd be alive to complain. You wouldn't hear a peep out of me if I were dead.
  #29  
Old 05-03-2016, 11:44 PM
pkbites pkbites is offline
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Originally Posted by Gray Ghost View Post
Have we done yet, the Second Chance guy shooting people with .308 while wearing his company's vests? (I'm wondering just what besides kevlar is in that vest.)
That doesn't look like soft body armor police officers typically wear under their uniform.
I went on the job in '82. I had a hard vest that was steel plates though not multi layered like that. It was worn over the uniform and was more tactical. My first soft vest was about circa 1984. I'm pretty sure the trauma plates were a type of ceramic though they were also covered in Kevlar so I couldn't be sure. They went in a little pocket in front of the vest in front of the Kevlar panels just like they are today. You wouldn't believe how much heavier that vest was (level 2) than todays level 3's. Todays trauma plates tend to be soft as there is a theory about bullets following a hard plate upward into an officers neck/jaw. Don't know if that's ever really happened.

About 1 1/2 years ago I was at a demonstration where a level 3 with soft trauma plates was fired at with .223 from an AR15. Went right through it. The vest was of no help whatsoever.
  #30  
Old 05-04-2016, 04:15 AM
Bear_Nenno Bear_Nenno is offline
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About 1 1/2 years ago I was at a demonstration where a level 3 with soft trauma plates was fired at with .223 from an AR15. Went right through it. The vest was of no help whatsoever.
3A.
I only nitpick because the difference between NIJ Level 3A and 3 is huge. It's the jump from soft armor to hard armor; from handguns to, well, those .223 rounds among others. Level III would have stopped them quite easily. IIIA doesn't stand a chance.
  #31  
Old 05-04-2016, 05:05 AM
pkbites pkbites is offline
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3A.
I only nitpick because the difference between NIJ Level 3A and 3 is huge.
Yep, you're right, it was a 3A. Typo.
  #32  
Old 05-04-2016, 08:18 AM
Chronos Chronos is online now
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Of course, "stopping a bullet" isn't a binary yes-no. It's also possible for a vest to let a bullet through, but still slow it enough that it turns a mortal wound into a survivable one.
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