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?
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.
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.).
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).
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.
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.
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.
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.
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;)
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.
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:
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.
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.
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.