Is there any one thing in particular? Or is it a combination of speed, shape etc?
From popular culture, I’ve picked up that teflon bullets are coated in the chemical so they “slip” through armoured jackets, but I know this to be a fallacy. What is the coating for?
I thought the Teflon helped the bullet slip through, too. At any rate, I think armor-piercing bullets have hardened steel shells that won’t flatten out like typical slugs do when they encounter Kevlar vests and such.
The faster, heavier, thinner, harder, and pointier the projectile, the more armor-piercing it is. Some of these are in conflict with each other (heavier & thinner, or faster & heavier, for example), so they have to get pretty inventive with exotic materials and techniques to accomplish this (discarding sabots, flechette rounds, depleted uranium, explosively-formed projectiles).
It lets them slip through the armor. Seriously.
OK, the ability of a solid projectile to break through a piece of armor is governed by a couple of factors. First of course is the speed. Faster is better. Next is mass. Heavier is better.
But there is an upper practical limit of how fast and heavy a bullet can be. All the omph that goes downrange is balanced by an equal amount of omph forced against the firer. In small arms almost all of this is transfered to the firer. Carried to an extreme, you could make a heavy fast bullet the destroys both the armor and the firer’s shoulder. That would not be good.
Even a heavy fast bullet can lack AP properties. the bullet must be quite tough. (Imagine a glass bullet. Heavy and fast, but it shatters on impact. That is also Not Good.)
So how do we increase the AP-ness of a bullet of a certain speed and mass? A couple of ways. The best is to put a heavy penetrator into the bullet. Imagine a little tungsten penetrator embedded into a light plastic bullet. The bullet weighs no more than a normal round. You fire it and the plastic coating rips away. Now all the energy that was in your normal round is still there, but is all in a really nasty little penetrator. Same energy in a smaller area.
Another trick is to reduce friction. The earliest AP rounds were normal rounds pulled out of their casings and reinserted blunt-end out. The round would hit the armor and the soft lead would lubricate the metal jacket (which would turn inside out) as it smacked the target. Better than nothing.
So the ideal small-arm AP round would be a teflon-covered penetrator made of tungsten or depleted uranium in a very light plastic casing that would strip away once out of the muzzle. Such rounds have been mooted, but they are expensive and hard to make. Their limited AP capacity does not make them worth the trouble.
Interesting. I’d actually heard of the teflon coating in a description given in the game Syphon Filter, later reading on another site suggested the AP properties of teflon were BS and it was just to reduce wear on the barrel of the gun.
The notion that simply coating a bullet with Teflon or some other friction-reducing substance to make them “slip” through body armor is about as absurd as the Fish carburetor.
The original, purpose designed armor piercing handgun round, the KTW .357 Magnum round (which despite it’s media and urban legand representation, was never sold to civilians, will not shatter or penetrate through a steel engine block, and has never killed any cop outside of a Lethal Weapon movie) was a conical, high velocity round made of tungsten, and was developed at the specific behest of the Department of Justice for FBI use. The pointed shape, hardness, and density are what gives it the armor piercing properties. It is jacketed with a thin layer of Teflon, which serves two purposes; one, it allows the rifling to grab the bullet (the harder tungsten would wear at the lands of the steel barrel), and two, it seeminly paradoxically helps the bullet grab hard, slick acutely angled surfaces like windshields which the bullet would otherwise ricochet off of. (The Teflon softens under pressure and acts like a momentary cane tip, keeping the bullet true and permitting it to break the surface of the windshield, albeit at the cost of stability.)
As for “armor piercing”; note that virtually any centerfire any rifle round will penetrate a Class II or Class IIIa vest by virtue of velocity and sectional density. (It is even alleged–though I’ve never personally been witness to it–that a .22WMR can penetrate such vests at close range.) Much military rifle ammunition is steel core and can easily pass through steel place of thickness in excess of .25in.
So all this bullshit about “spraying” a bullet with Teflon to make it armor piercing, or “cop-killer bullets on the streets” is good only for fermentation. If you want armor piercing, pull out Grandads old M1 Garand and get yerself a box full o’ surplus 7.62mm NATO. If you try going down to the local gunstore and asking for “a box of armor piercing bullets” they’ll laugh from here to Broadway.
Stranger
Well, most of the bullet never really touches the barrel, right? It is pointy and all that pointy stuff does not near to reduce wear.
The best site for Ammo Stuff is here and they are quite welcoming of newbies.
I’d heard that in WW1, German soldiers took up the habit of reloading rifle bullets into their shells base-forward to pentrate those new-fangled tank thingies. I’ve never encountered that explanation for their increased penetration. Instead I’ve read that it’s a matter of energy - apparently it takes less energy to punch a hole through a plate with a flat-ended punch than to swage a hole of the same size with a tapering, pointed punch. To be honest, I find both explanations a tad unconvincing.
Paul Kopsch, one of the inventors of the infamous teflon-coated KTW “cop killer” bullet claimed that the teflon actually reduced the penetration of the round through ballistic armour, and only served to increase penetration during oblique impacts with smooth surfaces.
http://www.scfirearms.org/2ndamend/ammo.txt
What he says in that interview is counter-intuitive, at least to me. He claims that the teflon coating makes a bullet less likely to deflect on oblique impact, which makes no sense at all. Except, a while back I was doing a literature review on sword construction for an archaological metallurgy thesis. I happened on an article where the armour-penetrating ability of a longbow firing arrows with bodkin points was tested on a steel helmet. One of the things being tested was the apparently historical fact that British archers used to place a bead of beeswax on the tips of these arrows for improved penetration. Trials showed that the beeswax improved penetration with oblique impacts. Again, this makes no sense to me since I would have thought the wax would make the arrow more likely to “skid off”, but those were the results reported.
And I see Stranger has read that interview already! I still don’t follow that “cane tip” analogy though.
As a matter of interest, the KTW bullet was originally made from sintered tungsten - very hard, with high density, but this was later replaced with hardened steel. There’s a kind of rifling that re-shapes bullets to a degree (polygonal rifling? not sure) and which couldn’t be used with the KTW rounds since they were too hard.
I am always pleased to learn new things. I certainly could be wrong. Ammunition is one of those things that seems to attract urban legends. Might I propose a change of venue to the Ammo website I cited? Perhaps there some Smart Guy can sight us in on the truth.
Most of the technical data has been covered in good detail, so it’s anecdote time.
I fire copper jacketed hollow points in my SKS. These will easily pass through 1/2" of steel from 50 yards. And they don’t even have a steel core.
Ditto!
I’m kind of reluctant to join another message board - I’m probably going to spend too much time simply reading that one. Good link! But if you’re already a member and want to bounce it off them and report back, go right ahead.
Me, too. I’ve also done what Stranger has mentioned…punching steel plate with my Garand. The jacketing usually hangs up in the hole, but the lead just slides right through to the other side.
Nitpick: Only modified and Navy Garands use 7.62N (7.62x51mm). Most use .30-06.
Under pressure, the Teflon (polytetrafluoroethylene or PTFE) becomes a viscous fluid, or technically a moltable polymer, which under the high instantaneous pressure between the bullet and the hardened surface allows (depending on who you are talking to) the tip of the bullet to dig in, or alternatively, allows the force of impact to be directed into the glass in a manner similar to a mud-pack on an explosive charge; in terms of basic physics, it changes the impact from a nearly perfect elastic impact to an very inelastic impact, and the glass surface, being more brittle, absorbs the energy and shatters rather than rebounding as it will tend to do at a shallow angle. Normal copper-jacketed lead bullets will just tend to flatten out, which both makes them stick better and reduces their penetration value; a 9mmPara or .38Spl roundnose will often deflect off of a windshield. The tungsten or hardened steel, however, will retain shape and will penetrate more cleanly; of course, the bullet will tumble after impact.
As far as I know, the FBI never issued these rounds to agents except (perhaps) in its own special tactics teams, but some police departments adopted them for SWAT units for a time. These days, SWAT teams have gone to using the .223 round rather than 9mm submachine guns because the former gives better overall performance while reducing excess penetration through common construction materials.
Note that the recently developed Heckler and Koch 4.6x30mm and the Fabrique Nationale 5.7x28mm SS190 rounds are small caliber, high velocity handgun/submachinegun/compact battle arm rounds that are touted as capable of being able to penetrate standard issue battlefield fabric torso armor (Class IIIa). They do so by virtue of being fast and having a high sectional density, at the expense of lethality of larger diameter or hollowpoint rounds.
Stranger
My bad. I actually started to write M-14, but then realized that Gramps probably doesn’t have an M-14 in the closet. The rounds have similar ballistics, though, and even the much less powerful 7.63x39mm round can easily penetrate the grade of torso armor worn by patrol officers.
Stranger
I found a wikipedia article on the FN P90, a gun in StarGate SG-1 as it happens which is why I looked at it, that mentioned the FN ammunition as being armour piercing. I thought that was why they were used against the armoured types in StarGate and then thought I may as well ask why 
Do your jackets ignite on impact? I’m always impressed by the shower of sparks that fly from this.
If fired at a target in the real world with nothing recording the event, it is highly unlikely.
If fired at a target in the real world with Hollywood cameras rolling, it will happen every time.
I think this has something to do with quantum physics, but can’t find a good cite.
Although the 5.7x28 mm round that the P90 uses supposedly can penetrate some armor, it is not as powerful as rifle rounds; a 5.56 mm round from an M-16 would be much better to penetrate armor and have more stopping power. I think the creators of SG-1 choose to use the P90 because it looks really cool, and on TV that’s all that matters.