Body armor is overrated

[ns66]

reading the sticky i was surprised to see so many folks think their ccw gun would be useless against him, simply because he wore body armor. i'd think anyone with ccw gun will be way better than nothing, a bullet even if can't penetrate, will hit like a hammer, that will save lives i am pretty sure

 

[Skribs]

The guy was high on pain killers, and the bullet doesn't have any more of an impact than the gun does on your hand. It'll hit hard, but not enough to really do much.

 

[hso]

will hit like a hammer

What makes you think that? TV/Movies/Games?

The physics is simple and simply doesn't equate to what you've been shown through "movie magic".

 

[monotonous_iterancy]

^ I've heard that most of my life about getting hit with a bulletproof vest on. I assumed that it could break bones.

 

[JohnKSa]

There's some potential for non-penetrating injuries through body armor, but that can be dramatically reduced by using trauma plates or even just heavy padding under the armor. The guy who invented the Second Chance vests used to shoot himself in the chest with a .44Mag to prove his vests worked. He used some padding/backing under the vest, no reason a bad guy couldn't do the same.

 

[dprice3844444]

even vest shots are going to hurt like hell.there is always shoulder,arms,groin,legs,knees, etc, to hit to slow them down or incapacitate them.that will give somebody enough time to possible reach/disarm them.standard training is to shoot center mass,if that doesn't work,you have to start getting creative.

 

[R.W.Dale]

A handgun will impart no more energy to the target than it does the firearm in terms of recoil.

A police handgun rated vest wearer may have some bruising because of the way Kevlar will follow the bullet as it traps and slows it.

A flak jacket or modern military grade armor with rigid strike plates it may be possible to not even notice a handgun round strike in the din of battle.

The murderer in CO had a body armor, groin protection, neck protection and a helmet.


To put this in perspective I can hit my steel target with a 5# shop hammer and swing it much farther than shooting it with a ccw caliber handgun

 

[Tom488]

and the bullet doesn't have any more of an impact than the gun does on your hand

Really? Plenty of LEOs have been hit in the vest, and broken ribs. I've yet to break, or even bruise, my hand, even from a .500 Magnum.

Said .500 Magnum has 3,000ft.lbs. of energy leaving the muzzle. If the shooter's hand were subjected to 3,000ft.lbs. of energy, said shooter's hand would cease to exist.

Due to the much greater mass of the firearm vs. the bullet, the recoil energy of the gun is only a few percent of the energy of the bullet. In the example of the .500 Mag, the recoil energy is around 65ft.lbs. or so

 

[Rubikees]

I am waiting to see the report on what type of body armor the person had. However, if he was shot at there is a possibility that the shooter would have paused while he had to replan what he was doing. That is if he did have the plated body armor. This pause might have given a person a chance to physically attack the shooter and neutralize the problem but we will never know.

 

[hammerklavier]

Said .500 Magnum has 3,000ft.lbs. of energy leaving the muzzle. If the shooter's hand were subjected to 3,000ft.lbs. of energy, said shooter's hand would cease to exist.

Sir Isaac Newton would be very surprised to hear this.

 

[mljdeckard]

There are so many variables that can happen, it's useless to 'what if' it after the fact.

A number of things may have made it good or bad to shoot him. If I had been there, maybe I would have been in the middle of the crowd that ran for the door. If I had dropped to the floor and played dead, and waited for a good shot, maybe I would have gotten one, maybe I wouldn't. Maybe I would have been close enough to take the head shot, maybe I wouldn't have. (I would likely have realized right away that he was in full armor, because I've used it myself.)

You know what the odds would have been if I weren't armed? Pretty much zero. I would have had to charge him, and hope that I reached him before he stopped shooting at the crowd and dropped me instead. Once I got to him, I would have to hope that I was better than him at hand-to-armed. I've trained in it a little bit, but I'm not great at it. If he shot me first, someone else would have to take the initiative and charge him again, enough of them would have to realize that the only way to stop him would be to make him split his focus, and know that some of them were going to hit hit to do it.

So, an armed attacker wearing full armor isn't a great situation, but shooting for his head is by far the best option.

 

[mljdeckard]

And yes, it makes a difference if he had trauma plates.

 

[denton]

The notion that the impact of a bullet against a vest is no greater than the impact of the firearm against the shooter's body is an old and incorrect notion. There are some things that happen that sound like that (force couples). But, as stated, the notion is wrong.

Consider a 180 grain 30-06 bullet launched at 2800 FPS by 57 grains of powder an an 11 lb scope and rifle combination. The kinetic energy is just north of 3,000 ft-lbs, if I've done my arithmetic right.

The rifle, on the other hand, has a free recoil speed of 9.51 FPS and a free recoil kinetic energy of 15.44 ft-lbs.

I have news for anybody that thinks those two produce the same impact or sensation.

 

[mljdeckard]

What news would that be?

What you are failing to remember is that when the force is concentrated to the size of a bullet, the target doesn't feel all of the energy the bullet carries, that's just how it works. As soon as the bullet hits the target, you are talking about momentum. Having body armor prevent the bullet from traversing the target would force the target to feel all of it, but it ripples, and the force is absorbed by the mesh or plates.

What the human target feels when hit by a bullet is the same thing as the firer of the bullet, plus energy absorbed by the weight of the weapon, energy required to cycle the action, etc.

 

[Warp]

Really?

Yes, really. It's fundamental physics.

 

[ns66]

Really? Plenty of LEOs have been hit in the vest, and broken ribs. I've yet to break, or even bruise, my hand, even from a .500 Magnum.

Said .500 Magnum has 3,000ft.lbs. of energy leaving the muzzle. If the shooter's hand were subjected to 3,000ft.lbs. of energy, said shooter's hand would cease to exist.

Due to the much greater mass of the firearm vs. the bullet, the recoil energy of the gun is only a few percent of the energy of the bullet. In the example of the .500 Mag, the recoil energy is around 65ft.lbs. or so

yes you got this right

the physics says the kinetic momentum (which is mass*velocity) must be equal for hand and bullet
but kinetic energy is mass*velocity^2, the bullet has much more energy distributed due to its much higher velocity than the hand

just a quick example to illustrate, assume bullet weight 1, velocity 1000, handgun/hand weight 100, velocity must be 10 (so m*v the same, law of physics)
the kinetic energy of the bullet then is 1*1000^2=1,000,000, while energy of handgun/hand is only 100*10^2=10,000

so the bullet has 100 times the kinetic energy as the recoil handgun/hand

 

[Warp]

yes you got this right

the physics says the kinetic momentem (which is mass*velocity) must be equal for hand and bullet
but kinetic energy is mass*velocity^2, the bullet has much more energy distributed due to its much higher velocity than the hand
just a quick example to illustrate, assume bullet weight 10, velocity 1000, handgun/hand weight 100, velocity must be 100 (so m*v the same, law of physics)
the energy of the bullet then is 10*1000^2=10,000,000, while energy of handgun/hand is only 100*100*100=1,000,000

Those numbers are useless.

For starters, you assume a handgun mass that is tiny. For a stoutly recoiling pistol many have experience with, let's take a .357 magnum firing a 125gr bullet. Do you know what the gun would have to weigh in order for the numbers to be anything like what you are trying to go with here? That would be a 2.86 oz gun. Go shoot a .357 mag, 125gr, HOT load out of a <3 ounce gun and tell us you didn't injure your hand. Tip: search for threads on the Smith and Wesson 340. People say it hurts like HELL to shoot with a hot .357 and stock grips, and it weighs about 12oz!

Furthermore, the area that force is spread over makes a big difference. Think about somebody in sneakers stepping on your foot vs somebody with a heal. Now think about the entire area of the handgun's grip vs the area of the bullet. Bullet resistant vests spread out the area of the energy transfer.

No more energy is transferred to the person you shoot than there is to you as the shooter. The mass of the gun changes PERCEIVED recoil, but the energy involved/transferred doesn't change.

Edit: Mythbusters has even done this one. They did as a Hollywood movie test (Hollywood lied again, of course), testing whether or not getting shot could lift you up off your feet and send you through a window...or even knock you backwards. The targets (such as pig carcasses) didn't even hardly visibly move.

 

[Texan Scott]

ahh, physics... the thing to remember is that we are not just measuring force in foot-pounds, but in foot-pounds per second per square inch.
Recoil of a firearm is theoretically equal to the force of the bullet - but experienced differently. The recoil of the gun is mitigated by the increased surface area of contact with the hand and slower motion of the gun (due to its greater mass) which distributes that force over time as well. Whereas a pistol distributes its recoil energy over 3-4 square inches over a period of time (however long it takes the gun and your hand to stop moving), body armor stops a bullet with a a very small surface area almost instantly.... same force, spread over less area and all at once. (that's why a bullet will go through your hand but a pistol won't).
The other thing to remember is that there's no way to predict exactly how body armor might distribute the stress of any given shot, or how any given person's body will handle that injury wherever located. All I can say is, I don't want to be the guy inside the armor when everybody's assertions on the subject get tested. Hit hard still hurts.

 

[CSC_Saint]

Coming from personal experience, I was hit by a round from a PKM on a pistol mag on the side of my plate carrier without a plate behind it. It knocked me on my @$$, and felt like I'd just taken a kick in the ribs from a UFC fighter. However, I was back on my feet a second later and back in the fight. The range at which I was hit was from 1600 meters away so I would say that it was comparable to taking a bullet from a pistol at close range. Does it hurt? yes. Can you still fight effectively? yes. I've also seen gunshot wounds to fellow soldiers in the groin area and they were still fighting until either treated or pulled out of fire. The only way to effectively stop a shooter in armor is a headshot. As seen firsthand, wounds to limbs do not always stop a fight. I have seen an iraqi shot twelve times in the grion and legs, while very much on his way to dead, still stay in the fight.

 

[ns66]

Those numbers are useless.

For starters, you assume a handgun mass that is tiny. For a stoutly recoiling pistol many have experience with, let's take a .357 magnum firing a 125gr bullet. Do you know what the gun would have to weigh in order for the numbers to be anything like what you are trying to go with here? That would be a 2.86 oz gun. Go shoot a .357 mag, 125gr, HOT load out of a <3 ounce gun and tell us you didn't injure your hand. Tip: search for threads on the Smith and Wesson 340. People say it hurts like HELL to shoot with a hot .357 and stock grips, and it weighs about 12oz!

Furthermore, the area that force is spread over makes a big difference. Think about somebody in sneakers stepping on your foot vs somebody with a heal. Now think about the entire area of the handgun's grip vs the area of the bullet. Bullet resistant vests spread out the area of the energy transfer.

No more energy is transferred to the person you shoot than there is to you as the shooter. The mass of the gun changes PERCEIVED recoil, but the energy involved/transferred doesn't change.

Edit: Mythbusters has even done this one. They did as a Hollywood movie test (Hollywood lied again, of course), testing whether or not getting shot could lift you up off your feet and send you through a window...or even knock you backwards. The targets (such as pig carcasses) didn't even hardly visibly move.

i revised my numbers to better illustrate, as you can see the energy difference is more dramatic
physics is physics, the kinetic energy of bullet is much higher that that of hand/handgun, that's just a fact

what people misunderstood is what must equal is the kinetic momemtums of two sides, the energy do not equal, in fact energy obey the energy conservation law which says the kinetic energy of bullet+that of handgun/hand=energy of the powder chemical reaction

 

[Warp]

i revised my numbers to better illustrate, as you can see the energy difference is more dramatic
physics is physics, the kinetic energy of bullet is much higher that that of hand/handgun, that's just a fact

what people misunderstood is what must equal is the kinetic momemtums of two sides, the energy do not equal, in fact energy obey the energy conservation law which says the kinetic energy of bullet+that of handgun/hand=energy of the powder chemical reaction

Oh boy.

I'll revisit at the end of the day tomorrow to see where this has gone.

 

[Texan Scott]

As the powder charge imparts equal kinetic energy to both objects, their kinetic energy will be equal, though differently stated. It is the gun's inertial momentum (the speed with which it accelerates/ decelerates) which varies in proportion to its mass. Energy will be the same at both ends.
All of this is getting away from the point of the post, however, which is that body armor is not absolute protection against all injury... a thing which I suspect we all knew without doing the math.

 

[holdencm9]

The energy will be absorbed into the armor. How efficiently it absorbs it will dictate how much it hurts the person wearing it.

Conservation of momentum still dictates "knocking a guy off his feet" or even down, or backward.

m1v1 = 115 gr x 1200 fps = 138,000

A person weighing 150 lbs will be weighing over a million grains. = m2, then v2 (the velocity of the person moving rearward) will be about 0.138 fps or under 1/10th of a mile per hour.

Same reason a 5 lb plate of steel will hardly move when shot with handguns. Maybe 3-4 mph.

It may hurt, it may bruise, but it won't do much beyond that.

 

[mljdeckard]

Here's how you prove it.

Take a 50 lb bag of cement, and stand it on a oil drum. Shoot it with a .45. Repeatedly if you want. Does it knock the bag over? Not usually. Why? Because there is more to it than just energy transferred.

 

[denton]

These discussions tend to go for quite a while. People tend to have some strange ideas that are pretty well fixed, and it's harder to shake those loose than it is to teach someone who comes in with a clean slate.

No more energy is transferred to the person you shoot than there is to you as the shooter.

As the powder charge imparts equal kinetic energy to both objects, their kinetic energy will be equal

These statements are categorically false, no offense intended. Kinetic energy absolutely does not divide equally between a relatively heavy (few pounds) firearm and a relatively light (fraction of an ounce) projectile. If it did, I suspect no one would ever fire a 30-06 more than once. See the recoil energy data I posted above. You can easily verify it for yourself.

Momentum is conserved. The total momentum of the firearm + powder + bullet before the trigger is pulled = the total momentum after if the rifle is freely recoiling, which it hardly ever is. A statement that the firearm and the bullet end up with the same momentum neglects the momentum of the powder/gas, and that is not a negligible term.

Force is the time rate of change of momentum. That's why recoil pads work. They spread a millisecond or so of recoil out over a longer time. There is less force to feel because the impulse (change in momentum) takes longer.

Force per unit area is pressure. Yes, pressure matters. There is a whole long discussion about the pressure a bullet exerts on flesh as it sheds momentum.

A bullet that strikes a trauma plate sheds a whole lot of momentum in a very short time, producing a lot of force. The trauma plate acts to spread this force over a greater area, but it is still enough that any reasonably stout round is going to feel like the business end of a bay mule. The force will generally be considerably greater than what the shooter feels, and it will be spread over a larger area than the shooter's palm or shoulder.