Product: Weapon: Gun
EFP Shotgun   (+2, -3)  [vote for, against]
A concave explosive disc is placed in front of a sturdy "breechblock" and detonates, sending projectiles forward.

This weapon is vaguely similar to a shotgun in that it has a stack of ammunition in a tubular magazine. That's where the similarities end.

A round of ammo is a thin concave layer of explosive behind a thin concave layer of copper. These are stacked in a tubular magazine that feeds ammunition forward to the front of the gun.

There, a simple mechanism is used to slide the round upward to where it's backed by a sturdy steel "breechblock". This block of steel matches the concave curve of the ammunition. The steel of the breechblock and the copper of the liner are used as electric terminals to detonate the explosive charge.

Since the explosive charge is surrounded on one side by the heavy breechblock and on the other side by the lightweight copper liner, almost all of the explosive energy gets directed into the copper liner. This accelerates the copper forward and inward at up to 7km/s, explosively producing several copper projectiles. For example, the copper liner could be scored so that there's one aerodynamic central projectile ringed by nine smaller "blobby" projectiles.

A stubby ring of thick metal around the edge of the round acts as a super-stubby "barrel", helping direct the sideways blast forward.

Due to the extremely high muzzle velocity, the ammunition can be lightweight and still have a good muzzle energy. Theoretically, such high velocities would be good for long range shooting, but explosively formed projectiles aren't sufficiently precise for that. Nevertheless, this gun can take advantage of the light ammunition weight and the low recoil for large magazine capacities and excellent full auto capability.

With 50mm x 3mm ammunition, a compact gun can have a 150 round capacity.
-- IJK, Mar 21 2007

EFP http://www.afrlhori...s/Dec04/MN0407.html
Explosively Formed Projectiles [bungston, Mar 21 2007]

<Edited for clarity>

The elegance of the EFP solution is that you don't *need* a breech, barrel, etc. I think you'd encounter all sorts of issues with this design;

Fuzing for EFP's, when using highly optimised designs, involves some fairly tight tolerances. You'd have to have a pretty reliable and exacting primer device.

The explosive layer is rarely as thin as you seem to beleive. A 50mm disc might have between 10-20mm explosive propellant.

The final velocity of 7km/sec is interesting. link?

How on earth do you expect to contain the pressures required to accelerate a projectile to several km/sec? Especially if you find some propellant gasses energetic enough to produce 7km/sec. If rupture isn't the issue, erosion certainly will be. The difference is that EFP's use high explosives, whereas normal bullets use typically low explosives, that have been retarded in some way to reduce the blast effects. I suspect you would have much trouble designing your backing plate and barrel-bit to be capable of withstanding detonation.

Are you expecting this to be a handheld weapon? You don't want to be near the business end of this thing. One advantage of high powered guns is that you don't need to be anywhere near the muzzle.

Lastly, there is a mathematical reason for EFP's being in the 100-300mm diameter range. If memory serves, there are reasons (due to shockwave shaping) that make it difficult to make a small EFP.

BTW EFP's are an exceptional engineering solution, they are entirely fascinating. EFP stands for explosively formed projectile/penetrator. No bone because I like to talk about them.
-- Custardguts, Mar 21 2007

The reason why current EFPs have a large block of propellant is because they're used in disposable one shot weapon warheads. It takes less mass to use a large block of explosive than back up a thin layer of explosives with a thick block of metal. Using a large block of explosive does mean the shockwave is not something you'd want to be near, but of course that's not a problem for the current applications (the warhead detonates near the enemy, but far from yourself).

For this application, you want the shockwave to be minimized, and you can afford to use a thick breechblock of metal because it gets reused many times. Thus, it makes more sense to use a small amount of explosive with the inert backing of a sturdy breechblock.

The 7km/s figure is an upper limit (potential speed acheivable with TNT), although you'd want to use a much lower velocity for greater efficiency.

The breechblock and barrel bit should be able to stand up to the beating. The required peak pressures are no greater than those in a rifle--this pressure is applied over such a large area that it still manages to accelerate the thin copper liner to the required speeds.

Compared to a 5.56mm bore, 50mm provides 80 times as much area. Thus, an equal peak pressure provides as much acceleration within 5mm as a rifle bullet gets in 400mm.
-- IJK, Mar 21 2007

Bun for introducing me to the concept of the EFP.

I would think the aerodynamics of such a projectile would inherently be less predictable than a tooled bullet or shell. Also, I cannot imagine that the barrel could be rifled. It seems to me these would be pretty inaccurate. Yes, I guess you said all that too.

I wonder if one could use that exploding jello capacitor principle to power these things. Then the ammo could just have jello, which would be safe and tasty. The gun would need a generator, though. It could be nuclear!
-- bungston, Mar 21 2007

[bung] I'll post the link if I can find it, but I read an article by a research group that had developed "aerodynamic EFP's". As the circular plate deformed into the narrow conical penetrator, it produced a circumfrential ripple at the rear (flared end) that had the effect of fins, stabilising the projectile. They were quoting accuracy of IIRC <1m at 200m range, velocity was I think about 4km/sec which is pretty good medicine for a tank.

Also the US's plans (are they implemented yet??) to use multiple EFP's as a sort of "area denial wepaon" whereby a bundle of them is dispersed by an artillery shell or cruise missile. They each float down by parachute, spinning away and scanning with millimetre radar. When they all have unique targets (they employ a type of swarm intelligence here..), they communicate and fire simultaneously. zap zap zap. No more tanks. It's really ambitious, but all of the technology is mature, so I wouldn't be surprised if they were ready to go by now.

[IJK] - whilst I'm sure you peak acceleration could be 80 times as much, as you have indicated, your impulse time is very short. If you want the smashingly high velocities you'll need some pretty steel-liquifyingly high pressures, because you'll always have a pretty short power stroke.

Also, not sure about these "thin copper liners". There is a minimum thickness, otherwise it all just falls apart while the penetrator is being formed. Kind of like a claymore.

And secondly, I imagine there is a lot of maths behind the use of a large ammount of explosives, not the least of which would be ensuring the duration of the explosion was long enough to sufficiently distort the penetrator, which is once again tied up in the whole resulting-velocity thing.

Not saying that there is no solution here, but you have a great deal of maths and computational modelling (or some really fun experimentation and extremely high-speed X-ray photography) ahead of you. Please send me an invite for the latter, I'd be glad to help/watch/drool.
-- Custardguts, Mar 21 2007

Having seen footage of EFPs in skeet rounds, and the large amount of explosion that /doesn't/ go in the intended direction, I don't think I want to be anywhere near this weapon when fired.
-- AbsintheWithoutLeave, Mar 21 2007

I wonder if you could simulate this with low explosives and foil?
-- bungston, Mar 21 2007

Without reading in detail, sounds similar to a chain gun or a claymore.
-- normzone, Mar 21 2007

sorry [norm], you should probably read it in more detail...
-- Custardguts, Mar 21 2007

You're right, it's neither fish nor fowl nor good red meat. Interesting, but count me on the observe-from-a-distance team.
-- normzone, Mar 23 2007

Apart from EFPs needed high explosives which have a cutting effect on metal (I.E. no breach would hold up) there is too much physics here that says this would not work. So I'll grant you that the mechanisms would indeed work without fail (Which, albeit preposterous, well soon see is a moot point) and use only physics to show you why this is a really really really bad idea.

First, EFPs slug velocity is closer to 4km/sec (Don't worry this actually works in your favor)

So lets assume you use 1 gram of copper, which is equall to 15.43 grains. (.223 bullets are about 55 grains)

Kinetic Energy (KE) is 1/2m(mass)V^2(velocity squared)

so we find KE to be (1/2)(.001)(4000^2) = 8000 joules (About 1475 joules less than a .338 Lapua Magnum whose recoil is very punishing in a large rifle)

Problem is the slug from your EFP would only be .112 cm cubed (Cu = 8.921g/cm^3) which if it where a perfect sphere would have a diameter of .6 cm (.236 cal) which at 4000m/sec would not cause a lot of tissue damage. In all reality it would leave a very small very clean hole, in and out, with very little energy transfer.

A bigger slug, you say?

2 grams of copper would only give you a .297 calibre slug but would have well over the KE of a .50 cal BMG round which is usually fired from a 121lb machine gun. What this all eludes to is:

Getting shot with this thing wouldn't be nearly as bad as shooting it.

(P.S. If your slug was comparable to the 1 oz 12 gauge slug the muzzle energy would be over 2X that of the GAU-12/U 25mm rotary canon)
-- MikeD, Mar 18 2008


Almost one year ago to the day I posted above a comment regarding chain guns.

I just Wiki'd the subject and it's not at all what I thought.

I was envisioning sequential loads of propellent and lengths of chain in a disposable delivery mechanism, as mentioned by William Gibson in "All Tomorrow's Parties".
-- normzone, Mar 18 2008

I'm just thinkin'... imagine a lower-powered version (say, lethal radius only tens of feet) with a curved backing plate, such that it can be thrown like a frisbee and detonated remotely. Then you've got a downward-firing grenade that can be thrown around corners.
-- lurch, Mar 19 2008

Is it just me, or does [mike]'s comment simply not say anything? I think he is getting impulse <momentum, recoil> confused with KE.

Which is not to say that he isn't right... A 50mm efp would probably kick your arse if you fired it from a shoulder mounted weapon. I had just assumed he'd build some kind of recoil-less feature into the design. I simply contend that you couldn't build a breech to contain the explosion.
-- Custardguts, Mar 19 2008

Is it your position, Custard, that muzzle energy is not coorelative to recoil? You and I both agree that the mechanics of this EFP Shotgun could not be engineered to withstand the detonation, but this point could be debated all day long. I chose, however, to argue with sound physics, to make the point that the effect of this theoretic weapon would be less to the target than to the shooter. Your 50mm EFP bazooka, on the other hand, albeit recoiless, fails by your own argument. *... if rupture isn't the issue, erosion certainly will be.* The whole thing (EFP shotgun), even if it could be done, would require efforts undue by several orders of magnitude when compared to the technology (I.E. the AR-15) that will produce the same (if not greater) effect.

And to Lurch's comment, I don't think you understand EFPs. They are not a 'kill radius' manner of weapon, like a grenade, but more comparable to a 'super armour piercing bullet'.
-- MikeD, Mar 19 2008

The small but very fast moving asymmetric projectile could still do a lot of shockwave damage to tissue. Against a tank it would probably not punch cleanly through but expend its energy complete against the armor - "good medicine" I think Custardguts called it.
-- bungston, Mar 19 2008

//I don't think you understand EFPs// - not at all out of the realm of possibility. However, since EFP is a development from research in armor-plate spalling when struck by shaped charges, it doesn't seem too far-fetched to believe that a shaped charge applied to the back of a scored plate might yield multiple fragments. Yes, you lose the extreme focusing effect that yields hypervelocity results, and that is why I posit it wouldn't shoot very far.
-- lurch, Mar 20 2008

In no specific order:

//probably not punch cleanly through but expend its energy complete against the armor // - At 4km/sec often overpenetration is the issue. Remember most antitank projectiles top out at 1.5 km/sec. The EFP has ~730% the kinetic energy per gram of projectile. And copper is rather dense. Sorry, it's just that the energy budget is so generous that yes, it burns up a lot of KE on the armour, then a bit more vaporising anything inside the cabin, then burns the rest blowing out the other bulkhead.

//Is it your position, Custard, that muzzle energy is not coorelative to recoil// Well, yes. Except in the whole "this has a bit to do with that" sense. Elemental kinematics says that KE <energy> is proportional to mass times velocity squared. Momentum <impulse, what you see as "recoil"> is proportional to mass times velocity. To take it to the extreme, imagine a 4g projectile going 1000 m/s. this has 2000 joules, but only 4 N*s of momentum. <equated as 4 newtons for a second, or 4000N for a millisecond recoil>. Compare this to a 2kg brick. If it has the same kinetic energy, it is traveling at 44 metres per second. But has 89 newton seconds of momentum <recoil>. if you find a gun that fires 2kg projectiles at 44 m/s, they will have the same KE as the gun shooting 4g @ 1000m/s. Would you think the resultant recoil was comparable? It would destroy you. So to answer your question, NO.

But anyway, we're arguing about the way in which we agree.

//the AR-15) that will produce the same (if not greater) effect// By the way, if you could make a "50mm EFP bazooka" it would certainly deliver more to the target than an ar15. In rough estimate, you could expect ~50g projectile @ 4000m/s, having 400 kilojoules of Kinetic energy. That's a shedload more on-target effect than any ar15 projectile. FYI, 20Mj is often touted as the 100% kinetic energy kill requirement for a frontal hit on a modern MBT. ie 20Mj will annhiallate any tank on the market, from any angle, 100% of the time. 0.4 Mj is a lot.

The idea's not realistic for a number of technical reasons, but if it were workable, it'd be devestating.
-- Custardguts, Mar 20 2008

Agreed, Agreed ...

You are absolutely right whereas the KE vs. Momentum is concerend. I regret having used KE. In recoil, however, you seam to not include the mass and velocity of the expanding gasses. Burn rate of TNT is not even in the same order of magnitude as Black Powder. And now, back to whiping that cold dead horse ...

your 50g, 50mm disc still equals **at most** .429 cal hole. At such a velocity, it's not even going to be a messy hole. Of the 0.4 Mjoules, just exactly how much do you think is going to be transferred to your intended target? (assuming it is not a tank) ****Less than a bullet of comparable calibre****

Leave the EFPs for armored targets and the bullets for people! They are used, as such, for a reason.

And Lurch ***Grrr*** listen: the shrapnel would go very very very far, just in **one direction**.

//However, since EFP is a development from research in armor-plate spalling when//

Lysergic Acid Diethylamide 25 (LSD) was first concocted to be a cure for scizophrenia. It's only useful application, now however, is to voluntarily cause the symptoms of scizophrenia.
-- MikeD, Mar 20 2008

Ok, I think we're all over it, but I really am curious. -Where do you get the //**at most** .429 cal hole// bit from? I hope we're not assuming that the disc magically transforms into a sphere here. 'cause it doesn't. I really wish that website that I used to look at was still up. It had really good photos of projectiles forming - done with x-ray strobes. You'd be able to see that the sectional density of the projectile is probably less than that of a sphere.
-- Custardguts, Mar 21 2008

And in conclusion: (One thing we can all agree on)

"High Explosives" and "Hand-Held Weapons" are two concepts that should never converge.
-- MikeD, Mar 21 2008

//two concepts that should never converge// probably need to adjust the tense of that statement. In WW1, HE bombs were being hand-dropped over the side of biplanes.
-- lurch, Mar 22 2008

random, halfbakery