Teflon coating on armor-piercing bullets

(my first question - oh boy!)

I tried looking this up on the net, I really did, but the people offering answers are either pro- or anti-gun lobbyists so their views are a little biased. I’m really just curious from a material science / engineering perspective (I’ve got opinions on guns, sure, but I’m not hellbent one way or another). I’m just hoping I can get the answer sans any axe-grinding. So here goes -

The two main characteristics of armor-piercing bullets are 1) they’re made of a hard metal like steel instead of a soft metal like lead. 2) They are coated with Teflon or some other dry lubricant.

The reason for using a hard metal is pretty much accepted - the bullet will deform less on impact and can more readily pierce the armor. It’s weather the Teflon coating does any good that’s the thorny question.

One school of thought says it does help with penetrating the armor. The lubricant helps the bullet cleve through the material. A rough analogy would be if you were trying to pound a steel wedge into a block of wood with a hammer, you could try putting grease all over it to reduce the friction on its sides as it pushes into the material (I could see all kinds of practical reasons why you wouldn’t want to grease a wedge like that, but you get the idea.)

Piffle, says the other school of thought - the Teflon has no effect on the armor. The only reason you need Teflon is to provide protection to the gun itself from being damaged by the hard metal used by armor-piercing rounds. The hard metal tends to strip the rifling on the inside of the gun’s barrel, which doesn’t happen with normal soft-metal bullets. Indeed, the Teflon can actually reduce the bullet’s ability to penetrate armor. One example I read was that when used on soft body armor the Teflon can become entangled with the Kevlar fabric (offhand that doesn’t sound right to me, but I appreciate the fact we’re talking about something impacting something else at several times the speed of sound, so the law of physics could be acting squirelly here).

So can anybody point me to some unbiased research studies on this stuff?

Entangled? The coating on such a bullet is very thin… almost just a paint, not a whole jacket such as the copper cladding on a lead projectile.

Now, the truth of the matter is that few makers of AP ammunition use “teflon” coatings.

Military AP rounds have a steel or tungsten core, but that core is typically clad in a copper jacket just as a lead-core projectile would be. The copper is soft enough to “engrave” into the rifling lands, and thus be forced to spin, but too soft to wear the ordnance steel bore appreciably.

The idea of teflon-coating came about years and years ago when some newspaper idiot hungry for a story happened across some KTW “armor piercing” handgun ammunition.

KTW made the bullet from semi-hard steel, pointed like a cone, and clad only in a thin wash of teflon (kind of like how a paper fast-food drink cup is washed with a thin plastic or wax.) The teflon was ONLY intended to reduce wear to the gun’s barrel.

Anyway, the reporter wrote his article as if the ammunition were designed specifically to defeat a police officer’s body armor. Thus the inflammatory label of “cop killer” bullets.

Except for the fact that the ammo was designed BY police officers (to penetrate car doors and other barricades in standoff situations- the name “KTW” is in fact the first initial of each of the designing officers) and was NEVER, at ANY time, available to civilians or anyone who wasn’t a card-carrying law enforcement officer.

What’s worse, is that due to the countrywide media hype of these “cop killer” projectiles and their so-called “intended purpose”, a great many current and potential thugs found out that a cop was likely to be wearing body armor, and thus, if they get into a shootout, they should aim for something besides the officer’s chest.

The hard fact of reality is that NO officer had, or has since, been shot with an “armor piercing” round… But dozens of officers have been shot in the head, groin, legs and shoulders, by perps who very likely knew the cop was wearing a vest.

Bottom line- no, the teflon does not help it in penetrating armor. In the case of the KTW round, much of the teflon would be worn off by the trip down the barrel, by the time it strikes the target anyway. But again, that’s a moot point, since no one uses teflon jackets on AP ammo, and the KTW isn’t manufactured any longer.

Kevlar vests work by distrubuting the impact over a larger area. A non-deforming bullet (whether it’s solid steel, solid copper, solid bronze, etc) focuses more of it’s energy over a smaller area, (it doesn’t spread out and mushroom) and even the mighty Kevlar strand can only take so much. In this case, a coating of teflon would be irrelevant. Might as well coat it with cream cheese for all the good it’ll do.

It’s the same as the old wives tale of dipping the bullet in cyanide or something. The amount that would be left on the bullet by the time it strikes the target, would be irrelevant and infinitesimal. Even the modern friction-reducing molybdenum disulfide coatings that are all the rage to apply to bullets right now, are predominantly wiped off the bullet by it’s trip down the bore.

I can only give you vague and anecdotal evidence, and
none of it appears to be unbiased. That said…

http://www.netside.com/~lcoble/2ndamend/ammo.txt

Conflicting info here - the first parts says they
won’t go through kevlar body armor, the later parts
talk about going through both nylon and steel plates.

When I took a gun safety class, my instructor said
he got his hands on some of these, put a bullet-proof
vest on a department store mannequin, and shot the
vest. He said they didn’t go through.

So, I don’t know. I’d say we need to do a real test,
but unfortunatly the teflon-coated bullets are presently
only for police and the military. They’re highly illegal
for civilians. I imagine the penalties are pretty bad if
you’re caught with them. (Maybe that’s why it’s so
hard to find published results…)

The other problem would be, regardless of whether the
bullet penetrated the vest you were testing or not, you’d
want to throw it away afterwards. A bullet proof vest
is weakened by being shot. Re-using it could lead to
vest failure - not a happy thing. The problem with this
is that I’m pretty sure bullet-proof vests are expensive.
I wouldn’t be happy to be out several hundred dollars
and a good bullet-proof vest just to see if these
things work. :stuck_out_tongue:
-Ben

Basically, teflon coatings are used for what you suspect. As a barrel protectant. That’s why some standard hunting bullets are teflon coated. It helps protect the barrel. With hard metal bullets, it protects the rifling and with soft metal bullets, it reduces the amount of fouling. An AP round is a hard metal, usually tungsten, bronze, steel cored, etc… In use against true armor, teflon does nothing. In use against body armor, especially the early types, teflon does offer a small advantage in the sense that it allows the bullet to reach a higher muzzle velocity, as well as retain a slight bit more velocity going through the layers that an “uncoated” bullet, but the advantage is pretty negligible in the actual penetration. In short, the stuff about spraying bullets with teflon to give them an armor defeating capability is all Hollywood creation. You’ll get a higher velocity, but basically nothing as far as a penetration advantage. Until last year, I worked for the government where part of my job was designing and testing guns and ammunition. That’s the only “cite” I can give you.

I did a bit of research on this subject in the past and came up with the following:

The KTW bullet was designed to go through hard armour, ie. car doors and windshields.

“The ordinary .38 Special service bullet would not get through the car door. And with any degree of obliquity, it bounced off the windshield. [Police] Lieutenant Turcus, Don Ward and I thought maybe we could design a bullet which would get through the car door, and get through the windshield and get the crook out of the car…” Dr. Paul Kopsch,co-inventor of the KTW bullet, in an interview in NRAction newsletter, Volume 4, Issue 5 (May 1990)

The teflon coating allegedly increases the penetration of the round versus hard armour, but decreases penetration v. soft armour.

"It helped bullets go through smooth surfaces, like windshields and car doors, especially at oblique angles. The former Army medical officer likened it to the teflon tip of a walking stick. It simply grabs better.
Kopsch: “Adding a teflon coating to the round added 20% penetration power on metal and glass. Critics kept complaining about teflon’s ability to penetrate body armor. That was nonsense typical of do-gooders. In fact, teflon cut down on the round’s ability to cut through the nylon or kevlar of body armor.”"same source as above

This is counterintuitive to me, I’d have expected a low friction coating to make the bullet more likely to glance off a hard oblique surface. However, I have seen similar reports in a different context:- I read an account in an archaelogical journal testing the ability of a longbow to penetrate steel sheet. They were testing “bodkin” points, which look something like a 4 inch nail with tiny notch barbs. Apparently, this is the sort of thing you’d shoot at men in armour.
The arrows were able to punch through the sheet if they struck it square, but failed to penetrate with oblique shots. However, if a drop of beeswax was placed on the point first, penetration was achieved at up to 35[sup]o[/sup] from normal impact. Again, this is the opposite of what I would expect and I’d love to hear why this works!

"the KTW round could penetrate at least some vests, but not because of the teflon coating.
"Kopsch: “It’ll defeat the ordinary ballistic nylon or Kevlar vest, but as I said, the teflon gives away its purpose and detracts from its ability to penetrate body armor.”"same source as above

So there is a little evidence that the teflon coating may help penetrate hard armour at oblique angles, although Kopsch can’t be regarded as an unbiased source regarding his own bullets. I suspect the role as a barrel protectant is more important, especially as the original KTWs were made from a very hard sintered tungsten alloy and couldn’t be used at all in polygonal twist barrels.

Welcome to the SDMB, mightyhumblehumble!

As you’ve gathered, the teflon coating serves purely as a lubricant to protect the rifling in the gun barrel. I’m too lazy to crank out a bunch of cites, but I can say that I’ve never seen anything written to the contrary, outside of propaganda put out by an agenda-driven organization.

I should point out that the OP contained a few oranges mixed in with the apples. Soft body armor will not, and was never designed to, withstand a projectile “impacting… at several times the speed of sound.” The big scare a few years back over the KTW bullets was all about handgun ammo, which typically launches a slug at only slightly supersonic or even subsonic speeds – the .38 Special, for example, generally produces a muzzle velocity around 900 fps, with impact velocities being somewhat lower depending on range, etc.

AP ammo for military use is generally rifle-caliber stuff, .30 and larger, traveling at multi-sonic speeds. These bullets will go through soft body armor – and the person inside the armor – almost as if they weren’t there.

I just want to point out that almost any round shot from a rifle will penetrate a kevlar vest.

Vests are specifically to protect the officer from light to moderate handguns, which make up the majority of the weapons carried by criminals.

Keep in mind that the average criminal has very little training with his weapon, and probably has no clue about ballistics.