BOOM! Shot in the Kevlar: How effective?

Factual Questions
1

Seeing the recent ‘Pacific’ TV series, the Marines have no body armor, just an undershirt. Thinking about today’s armed forces, at least how they are portrayed in the movies (where historical accuracy is more important than box office receipts), it strikes me as the equivalent of going around nude, if you don’t have some series Kevlar.

So, how effective are these Kevlar brand armor? Are all the types of ‘bullet proof’ vests the same? Or are some thicker than others? What kind of bullets do they stop, and at what distance? If the bullets penetrate, are they significantly less deadly even so? Or does it matter? Are there (small arms) bullets that can entirely overcome this armor, like ‘exploding’ or special rounds?

2

Someone will be around in a minute with some better info I’m sure, but for the basics:

Kevlar is a trademark name for a material, not a a brand as such. It’s the same as Teflon in that regard. And in the same way that you can’t buy Teflon brand frying pan or iron but can buy a GE or Pansonic brand made with Teflon, so you can’t buy a Kevlar brand vest (AFAIK) but you can buy dozens of brands made with Kevlar.

And the quality and construction vests containing Kevlar varies immensely.

Following on from the above, the construction of vests varies immensely. It’s not primarily an issue of thickness. Vests are “tailored” in different ways. Some are easier to move in. Some provide protection to the groin, neck and shoulders, some don’t. Some are made in multiple, modular pieces so that you don’t have to discard the whole vest as it wears or is shot, others don’t.

More importantly, many have added materials aside from Kevlar. The most basic vests are only Kevlar, but the more expensive (and effective) vests are composites with layers of titanium, ceramic or gel sandwiched with one or more layers of Kevlar.

Depends on the vest.

A Kevlar only vest is of limited use in a war. It will stop shrapnel or a handgun round but has no hope at all of stopping a standard rifle round at anything less than half a mile. And if a rifle bullet goes through you’re worse off than if you had been wearing nothing. An unimpeded rifle round will often go in one side and out the other. A round striking vest might lose enough energy to stop in you, or even start tumbling. So a Kevlar vest is of some use in war, but the weight and the amount that it restricts your movement probably make sit worse than nothing for infantry.

The composite vests vary a lot. The best of them are a sandwich of ceramic, kevlar and titanium plate. The idea being that the ceramic shatters, dispersing most of the energy, the titanium then catches the bulk of the slug and the Kevlar catches the fragments. These will (allegedly) stop a rifle round at 100 metres if it strikes at an angle of greater that 15o (IIRC). So if it performs as advertised it would probably stop most of the stuff fired at you, depending on how close quarters the fighting is.

These types of vests also greatly reduce the energy of the bullet even if it does get through, though once again it’s debatable whether you’re better off being hit by an intact, full speed bullet at 20 metres or by a tumbling fragment travelling at low speeds.

What do you mean by small arms? No usable armour will reliably stop a square hit from a rifle round at close quarters. And that’s just as true of rifle rounds in 1890 as it is for modern assault rifles. You don’t need anything special, a stand metal-jacket rifle round will punch clear through body armour.

In terms of handgun rounds, any decent body armour will stop them. Hollywood to the contrary, “Teflon bullets” and “exploding bullets” don;t go through armour. “Exploding bullets” for handguns are basically glorified dum dums designed to shatter on impact, and are even worse at penetrating armour than standard rounds.

3

Wikipedia on classification standards.

The vests that police wear are effective at protecting against many pistol rounds. All but the smallest rifle rounds go right through; “cop killer bullets” is a meaningless term used by people with an agenda or who don’t know any better.

The military and SWAT-type groups use Kevlar vests supplemented by ceramic plates which can protect better against more powerful rounds. The US army uses IOVT and the Marines use MTV.

4

Hijack warning, Kevlar would make for a very tough zombie. So my contingency plan for the impending zombie apocalypse is to wear six layers of Kevlar, and one of those SWAT suits, and wield a machete. Then go berserk, and get bit by a zombie, and probably get turned. This would confuse, and probably terrify other survivors.

5

What’s so different about rifle rounds? Do they use a lot more powder?

6

Bullet resistant. Bullet resistant, not bullet proof.

It may seem like a small distinction but if you contact a manufacturer of vests or glass enclosures or such, and you ask for bullet proof they will politely correct you that the products are bullet resistant. Any of these products can be penetrated at some point.

The first time I contacted a manufacturer asking about a bullet proof window for a drive thru I was carefully corrected that the products were resistant. They were gently insistant that I refer to it that way. I got the definate feeling that the order was not going to procede unless I acknowleded that I understood.

7

They use more powder, they travel a lot faster due to the longer barrel, they are typically tapered into a point (whereas handgun cartridges are not), they are much more spin stabilized, and they are of a smaller caliber (smaller diameter).

All of the above contribute to the far more exceptional ballistic performance of a rifle when compared to a handgun.

Here, see for yourself.

8

A Police buddy of mine got shot by a pistol in his vest. He said it was like being hit in the chest by Catfish Hunter’s best fastball. It really hurt and knocked the wind out of him, and left a bruise. But he was alive.

9

In case that doesn’t make sense to anyone (greater friction, etc.) let me explain:

A bullet is moved by expanding gas. At some point the gas has expanded as much as it is going to and just doesn’t have any more push. But, for some amount of time it does have plenty of push to add, accelerating the bullet more and more. An average pistol barrel is too short to allow the maximum expansion to get all of the juice there is to be gotten from the gunpowder. Just sticking a regular 9mm bullet in a longer gun will get you a faster bullet than you would get from a pistol.

10

Yes, I suppose I could have explained it in more detail. So I will, in (very) simplified terms.

The tapered point and the smaller diameter is roughly analogous to being hit by a pin instead of an unsharpened pencil. In addition, the drag coefficient is reduced so less speed is lost. Since the bullet is already traveling faster due to the advantage of the longer barrel, it has more energy at the point of impact, and the shape drives the bullet right through the target.

The spin stabilization is a function of the lands and grooves of the barrel, also known as the rifling. Rifles and (most) handguns have established ratios for the number of turns per distance traveled. An AR-15, for instance, can have a 1:9 ratio, which means that the bullet will twist in the barrel one time per 9 inches of travel. The spin imparted causes the bullet to travel greater distances with more accuracy and maintained speed.

A handgun has all of these characteristics, but due to the compactness of the weapon and the need for a smaller action, round-nose or truncated-cone bullets are more typical, which provide more atmospheric resistance. They also generate less muzzle energy and do not spin as quickly, so they are not typically long-range weapons. It is possible to chamber a handgun for a rifle round, but a handgun will never outperform a rifle in the came caliber.

There, that’s better.

11

It really has as much or more to do with stopping shrapnel as it does bullets. Most fatalities in Iraq and Afghanistan are from IED’s.

12

Muzzle Velocity is a function of barrel length

13

This isn’t wholly accurate. Handgun rounds penetrate lots of things better than rifle rounds. The pointiness of the bullet doesn’t have anything to do with its armor penetration; that is a function of sectional density and total energy and bullet design. Hollowpoints want to put all their energy in the first thing they hit, FMJs don’t. That’s the whole point of expanding bullets, in that they don’t waste time penetrating, but give up all that kinetic energy as fast as possible.

If you make bullets out of hardened steel, they will penetrate better than hollowpoint copper/lead bullets, even if shot out of a pistol instead of a rifle. The damage it does to a person won’t be nearly as bad, though, because you don’t get the sorts of enormous wound cavities you do with expanding ammo.

Rifle rounds will penetrate a vest better than handgun rounds simply because a rifle cartridge has at least twice the velocity and a lot more energy (KE = mv^2), all things being equal. Bullet shape has very little to do with it, because every type of round (other than armor piercing rounds) starts deforming the instant it hits.

14

First off, I did say that it was an oversimplification. If you want to make it uber-complicated, be my guest.

Second, there is nothing that a handgun round penetrates better than a rifle round. It can be absolutely, repeatedly demonstrated that a rifle will outperform a handgun in every caliber. If you chamber a rifle to fire handgun ammunition, essentially making a sub-machine gun, it will outperform a pistol firing the same ammunition. Every time.

15

Very cool link. The dents in the clay. . .ouch.:cool:

16

Not quite true here. The Box of Truth tested various rounds against boxes filled with sand and surprisingly the 9mm and .45 rounds made it farther than the 5.56 & 7.62x51 mm rounds. Basically the faster moving round fragmented when they hit the sand, quickly dissipating their energy, while the slower moving bullets held together. It probably wouldn’t be too hard to find a caliber were firing it in a rifle causes the bullet to move fast enough to fragment, while the handgun version of the exact same round moves slow enough to not fragment on impact, and thus penetrate better.

17

Incorrect. Penetration is in large part due to the bullet not deforming or fragmenting. A slower round does not have as high an energy budget to start this process.

Handgun rounds will penetrate drywall sections much more readily: http://how-i-did-it.org/drywall/results.html.

You need to define “performance” here, when comparing apples and oranges. If you get, say .45ACP to come out hot enough, you will decrease drywall penetration because the round will deform or fragment enough to transfer most of its energy when it hits something.

There are obviously differences between drywall and body armor, but the same principle applies, in that to penetrate a vest you want to deliver all of the kinetic energy possible into the vest. A rifle simply has a lot more energy to deliver. For something softer, like people or drywall, penetration and damage are generally exclusive and dependent upon bullet design.

ETA: also what RandonLetters said.

18

So what is the purpose of coated bullets?

19

They keep your barrel cleaner.

20

And to reduce barrel wear, which is somewhat related.

If “Teflon bullets” are any better at penetration, it’s because of the bullet itself and not the Teflon. A group (including a police officer) designed a round that had better penetration due to a brass core. They added Teflon because brass is harder than lead and thus is harder on the barrel. Adding Teflon alone does not make the bullet noticeably faster or more powerful.