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Mr. Bill 04-30-2016 07:41 AM

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?

Sasquatch 04-30-2016 08:19 AM

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.

AK84 04-30-2016 08:34 AM

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.).

Snarky_Kong 04-30-2016 12:17 PM

Quote:

Originally Posted by AK84 (Post 19296007)
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.

Raguleader 04-30-2016 12:43 PM

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).

albino_manatee 04-30-2016 05:26 PM

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-

Ranger Jeff 04-30-2016 07:48 PM

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.

Chronos 04-30-2016 07:55 PM

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.

Stranger On A Train 04-30-2016 08:29 PM

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

jasg 04-30-2016 09:04 PM

Quote:

Originally Posted by Stranger On A Train (Post 19296993)
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?

Bear_Nenno 04-30-2016 09:06 PM

Quote:

Originally Posted by Mr. Bill (Post 19295963)
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.

Stranger On A Train 04-30-2016 09:37 PM

Quote:

Originally Posted by jasg (Post 19297059)
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.

Stranger

pkbites 05-01-2016 02:41 AM

Quote:

Originally Posted by Bear_Nenno (Post 19297062)
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! :eek:

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! :D:p;)

Bear_Nenno 05-01-2016 04:13 AM

Quote:

Originally Posted by pkbites (Post 19297384)
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.

Ranger Jeff 05-01-2016 04:26 AM

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.

Bear_Nenno 05-01-2016 04:48 AM

Quote:

Originally Posted by Ranger Jeff (Post 19297441)
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

Hail Ants 05-01-2016 05:16 PM

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.

Siam Sam 05-01-2016 11:01 PM

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.

Martini Enfield 05-02-2016 08:16 AM

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.

lost4life 05-02-2016 12:17 PM

Obligatory Archer link.

skdo23 05-02-2016 03:15 PM

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.

Chihuahua 05-02-2016 03:43 PM

Quote:

Originally Posted by skdo23 (Post 19300398)
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.

Enright3 05-02-2016 03:44 PM

Quote:

Originally Posted by skdo23 (Post 19300398)
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

Gray Ghost 05-02-2016 06:01 PM

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.

Isilder 05-02-2016 08:42 PM

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... )

Bear_Nenno 05-03-2016 01:09 AM

Quote:

Originally Posted by Gray Ghost (Post 19300821)
(I'm wondering just what besides kevlar is in that vest.)

In 1984? It's most likely steel trauma plate inserts.

Raguleader 05-03-2016 08:41 AM

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.

Boyo Jim 05-03-2016 10:05 AM

Quote:

Originally Posted by Ranger Jeff (Post 19297441)
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. :p

pkbites 05-04-2016 12:44 AM

Quote:

Originally Posted by Gray Ghost (Post 19300821)
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.

Bear_Nenno 05-04-2016 05:15 AM

Quote:

Originally Posted by pkbites (Post 19304547)
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.

pkbites 05-04-2016 06:05 AM

Quote:

Originally Posted by Bear_Nenno (Post 19304786)
3A.
I only nitpick because the difference between NIJ Level 3A and 3 is huge.

Yep, you're right, it was a 3A. Typo.

Chronos 05-04-2016 09:18 AM

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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