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The most powerful mobile electromagnetic railgun built by a non-government (imgur.com)
304 points by nkurz on Nov 10, 2015 | hide | past | web | favorite | 147 comments

This is absolutely not 27,000 joules. 27,000 joules would produce a temporary wound channel nearly large enough to destroy the ballistic gel block, and then it would travel through the entire block, sending the block a foot or two into the air. Based on the penetration of the projectile into the gel, but taking the obtuse nature of the projectile into account, I'm left to conclude this was more along the lines of 1000 joules... which makes me think the "50mph" that the author claims the CO2 provides might be more along the lines of 200mph, and that the magnetic acceleration aspect of the gun is actually doing nothing at all.

In other words, we might be looking at a slightly high-powered potato gun being described by a misinformed author. Don't believe me? Take a look at the delay between the shot and the entry hole in the car door gif. That's commensurate with a projectile moving at freeway speed, not something with 27,000 joules, which for an aluminum projectile at that size, would be something like +4,000 feet per second.

EDIT: Updated mph to take @avian's math into account - the ballistic gel penetration supports that as well.

Let's see. The webm video of the car door shot is 30 fps, with each frame repeated 4 times. This suggests that original was shot at 30 fps and then reduced to 1/4 speed.

The delay between the first flash from the gun and the entry hole appearing is 4 frames at original fps. At 30 fps, that gives flight time between 100 and 130 ms.

I estimate that the distance from the gun to the car door is around 10 m. That gives speeds on the order of 100 m/s (200 mph).

Energy depends on the mass of the projectile. At these speeds, 27000 joules would require mass in the range of kilograms, which is obviously not true. Still, it seems feasible to me that this gets better than highway speeds.

Paintball guns are usually limited to 300 feet per second in competition- that's 91 meters per second, which is about what you are measuring.

A paintball weight 3grams, whereas the rail gun projectile is 11 grams. Paintball guns can shoot faster than is competition legal, and the much longer barrel could allow it to add more energy than it could with a heavy projectile in an equivalent paintball gun.

Um, no. A paintball weighs about 3 grams [1].

[1] http://www.dtic.mil/dtic/tr/fulltext/u2/a473706.pdf

Thanks! Corrected.

At least I wrote the wrong measure on both, so the ratio was still right.

They say that the paintball gun doesn't shoot the projectile fast enough for it to overcome friction from the rails, so without the magnetic field it wouldn't exit the gun at all, which seems plausible. So assuming they are trustworthy you can completely discount the energy provided by the painball gun when considering the energy given to the projectile.

It's probably 27kJ measured by the stored charge in the capacitor... which probably aren't delivered to the fullest extent.

You can see the wires jump--that's inductive magic in action. To get any sort of quick magnetic pulse into the railgun, you need high voltage[1] and low transmission line inductance; neither of which are satisfied here.

A guy I know works on high power pulse mode lasers and they achieve ridiculous rising edges with thin twisted pair wire. Lots of resistive loss but hey at least the current rising edge is nice and fast.

[1]: a few kilovolts.

It's probably 27kJ measured by the stored charge in the capacitor... which probably aren't delivered to the fullest extent.

When this was on Reddit yesterday the OP did a mini-AMA in the thread [1], and he confirmed this.

27kJ is the stored charge the capacitor bank. For various reasons, he's vary aware this is not all transferred to the projectile.

[1] https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_gian...

Perhaps it is, but the inefficiency of the machine shouldn't really come into play when describing how powerful it is. Otherwise, I could call my car a 900 horsepower Honda Accord, based on the gas it burns, since the engine probably isn't even close to 30% energy efficient.

They actually typically report horsepower and torque measurements for cars at the engine and not at the wheels. There's an additional efficiency loss in the drive train not accounted for in marketing numbers.

I think a lot of the energy is going to heat since the blocks of Aluminum melt and even vaporize.

I didn't mean inefficiency, I meant that not all of the energy can be delivered to the projectile because the delivery is rate-limited because of electric properties.

Also, there is inefficiencies in play, such as the melting aluminum like the other person suggested.

I think it's because the bullet can't withstand the current/pressures and melts/vaporizes.

Edit: also note that these are high speed camera recordings.

"The power must be monitored and disconnected before the maximum rating of the capacitors is exceeded!"

As a teenager I used to love plugging in little electrolytic capacitors into the wall socket. Like, rated for 16v capacitors hit with (in australia) 240v AC. Man those things explode big time :-)

I did actually try this with big capacitors (still low voltage) hoping for a proportionally bigger explosion, but those guys just fizzled.

Alright, just about now I'm thankful the internetz didn't exist back then i could have done some real damage to myself. This rail-gun looks stupidly dangerous.

It doesn't take mains voltage to get electrolytic capacitors to fail catastrophically. Just reverse the current. (Or rather don't).

Nearly lost an eye when a kid I was paired up with in science class made that mistake. The cap blew off with a loud bang, and I was left with a perfectly symmetrical round bruise just above my eyebrow.

I never forgave him. Not for nearly blinding me, but because he was happy to let everyone believe it was me who had made the mistake!

In theory big capacitors have vents so they should fizzle rather than explode.

Even small ones (47uF or so) have safety slits to release overpressure. Maybe that's a recent change, though. I don't think I have any caps older than about 20 years, so I can't verify.

Many things are being asked that were answered by the creator in the Reddit thread yesterday.


Yeah, only posting the image thread misses the main discussion. Thanks for the link.

> Two years were required to acquire 56 of this capacitor (This project began in February, 2013). Two more capacitors were purchased as backup, in case of failure. The total cost was $2,600. The MSRP on this type (new) is approximately $850 per capacitor ($50,000 in total).

My question is who does that and cheaps out on the copper to connect them?

That's a lot of expense on capacitors. When we made a rail gun at school, we built our own capacitor bank with big glass cider bottles. Main problem we had was the projectile (ball bearing) welding itself to the rails. Solved by rubbing them with graphite before each firing. No idea what the efficiency was, but we lodged several bearings deep in a brick wall.

They made us dismantle it as it was unsafe - so we re-use the capacitors and made a tesla coil.

"They made us dismantle it as it was unsafe - so we re-use the capacitors and made a tesla coil."

Actually laughed out loud at this.

own capacitor bank with big glass cider bottles

What was the construction of these - plate inside/outside made of foil?

Be careful with Leyden Jars - they can self charge. At size (like a 5 gallon bucket), they can carry enough charge to seriously hurt you.

Anodised aluminium foil, borax for the electrolyte. Think we had about 30 of them. Definitely not a portable setup!

That graphite trick sounds pretty spiffy, thanks!

Aluminium is a better conductor by weight, maybe that's why?

Not by volume, though; aluminum has about 1.5 times the resistivity of copper. Aluminum also has a much lower melting point (660°C vs. 1084°C) and is also very prone to galvanic corrosion when used with other common conducting metals.

That looks like a really fun gizmo. I'm surprised it took him that long to get the capacitors though. Another fun way of storing energy is a flywheel on an axle driving a generator. You can mechanically get the flywheel up to speed while the coil of the generator is open circuit, and then power your apparatus with it by shorting the output coil. If I did the math right and you used an old 20" car rim and weighted it up to 25kg (55 lbs) you would need to spin it at 2,500 RPM to store up 27kJ of energy. Lawn mower motor could do that, I've seen it on Battlebots :-).

But perhaps more interesting slug. The NRL uses a conductive "sabot" in the gun which then launches the projectile (which is not plasma at that point) our the end. Seems like some improvement to be made there.

Also there is the issue of erosion of the gun rails. How many shots before you need new rails?

The best thing though is the really awesome small talk at parties, "I was tuning up the rail gun to manage the shock wave that develops on the leading edge of the slug when it goes supersonic in the barrel you know? And then I noticed hey, the plasma is creating a partial vacuum from the heat, and the shock wave I'm seeing comes when it hits the air at the end of the rails, and I think hey someone has to have solved this problem ..."

I suppose the author counts the University of Texas as being government? They were able to propel a 185g projectile at 1900m/s which is nearly 700kJ of projectile energy, wheras this appears to be at best 1kJ of projectile energy.

[edit] Just found that in the 80s they achieved an 8.8MJ launch; their later designs were lower energy but could fire repeatedly.

I believe the UT people are also behind the US Navy's railgun project. They also developed a railgun howitzer in the 90's. Perhaps that qualifies them as "government".

I didn't realize they were behind the Navy one too; it would be interesting to hear why they switched from flywheels to capacitors for power delivery.

HV capacitors seem to be cheap here (Shenzhen). I guess I know what's my next side project.

Better get real good life insurance. I think most people fail to see all the dangers in this project. This thing terrifies me and wouldn't be within 40 feet of those capacitors. Electricity doesn't always behave the way we intended it, and this would probably be fatal if it discharges incorrectly or accidentally.


Even though this project was very cool to watch, but it looked super dangerous to me, especially the capacitor bank - it looked very ghetto.

You're right, of course. I was making a joking remark here. I had enough mishaps with small HV capacitors in my childhood to know how incredibly dangerous this stuff can be (as if wasn't obvious from the sparks of molten metal on every animation there), especially that you're going to stack the capacitors to ramp the voltage up to dozens of kilovolts.

> Better get real good life insurance.

I strongly suspect this sort of thing is exempted in most life insurance coverage (like skydiving and flying general aviation planes usually are).

> This thing terrifies me and wouldn't be within 40 feet of those capacitors.

Good for you. Sailing around the world hundreds of years ago was dangerous. Going to the moon 45 years ago was dangerous, tons of things are still VERY dangerous.

Just because it's beyond your personal level of safety-acceptance, it doesn't mean there are not hundreds of people lining up to do it. You mentioning it's dangerous adds absolutely nothing to the discussion or possible learning opportunities.

All you're doing is detracting from someone who's actually doing something. Rather than being so negative, why don't you go out and do something and document it as well as this guy and share it for everyone like he has?

All you're doing is getting pissy at someone who has pointed out legitimate safety concerns. You think sailing around the world didn't involve planning and safety considerations, or that going to the moon did have a safety talk or two? Yeah, there are always people lining up to do things. And sure, plenty of risks were taken. But there's absolutely nothing wrong with thinking about safety. They didn't say they wouldn't do it, they said they would maintain a safer distance.

> They said they would maintain a safer distance

And I like tofu.

Neither of those pieces of information add anything useful to the discussion.

Why doesn't it? There are plenty of instances where bad safety practices with high energy have led to injuries. In fact, the parent comment had more information relevant to the discussion than yours did. By your measure, your comment brought absolutely nothing to the discussion, and you would have been better to simply ignore the comment you didn't like. Policing what people say in that manner is subjective and tends to lean more towards your personal dislike for the comment than for any stringent criteria of quality. All that said, I like tofu too. Maybe we can find a tofu discussion on HN to carry on in.

It bugs me that so many posts on HN immediately get shot down with "It's not safe", which is not constructive at all.

(see: self driving cars, drone delivery, etc.)

Just saying "it's not safe" is not useful, and I suppose I wish people would do it less. Yes, safety is a consideration for sure, so a comment that talks at length about how to make it safer is useful. Simply saying it's not safe is not constructive.

We should have a HN tofu meetup

Fair enough!

Maybe your next side project should be an assembly robot to assemble and operate the railgun for you, maybe inside of a concrete vault with Lexan around it. Then the railgun could be the project after that.

What's their quality control like, though?

"During the second test, the projectile snagged before fully entering the rails and was partially reduced to a molten spray of vaporized aluminum. This issue was resolved for future launches with looser fit tolerance."

For me a machine that can create a molten spray of vapourised aluminium (fixed spelling) is actually almost as interesting as a rail gun. :-)

Dear FBI, purely for artistic purposes.

The discovery of the elements is an interesting story. Even better, is all the craziness surrounding the naming of the elements! There are two (classical) naming methods for elements we care about for this story: those elements whose names end in -ium (strontium, gallium, et al), and those elements whose names end in -um (platinum, tantalum).

Humphrey Davy (the discover of Al) originally use aluminium (1808) but, later, switched to aluminum (1812); the latter spelling became his preferred spelling. The British objected to the -um variant, and insisted on -ium. Davy (himself) seemed to consistently choose the -um variant after 1812.

When the mass production of Al became feasible (another great story!) the inventor (... or, most effective capitalizer, I guess), used the -um variant; this happened in North America. Since that was the effective product name, it became the most commonly used variant in North America.

Now, which is correct? The answer is: both! While I only have a few examples to look at, the dictionaries I have admit both spellings are used, and note which spelling to use in which circumstance, i.e., aluminium in Britain, and aluminum in North America.

In fact, for some programs if your English locale is US then 'aluminum' is recognized as the proper spelling, and 'aluminium' is marked as 'misspelled'. However, switching your locale to UK, the opposite is true!

The original name given was not "aluminium" (nor "aluminum"), but "alumium". Wikipedia confirms this and provides citations.


The story I've heard is that Davy started with "alumium", but added the "n" because the pronunciation was deemed too awkward, yielding "aluminum". Others pushed for "aluminium" because it sounded more consistent with other elements' names.

Unfortunately I can't edit my post; I would add that I am repeating a story I have heard---it is broadly the same as Wikipedia, as you point out. I am certainly not an authority!

Best thing about this railgun is the optical effect. The spark shower looks like a really cheesy science fiction movie.

Also if you're not concerned about the 330fps legal limit paintball markers are manufactured to you can probably adjust the regulators (not just the velocity screw you mentioned) to get a much higher initial kick. Or possibly use your own valve, that tank must output around 400-800psi before the marker regulates it down to somewhere like 200-300.

And avoid feeding liquid CO2 into the marker. If there's a siphon tube in the tank it's fine that way up otherwise have the valve pointing up-ish.

Somebody buy that guy a high speed camera.

The coming decades will surely going to be interesting as we are getting better at arbitrarily manipulating matter in a cheap way. It seems to me that the power of the individual could just become too big. There is a good reason why we decentralize important decisions: Decisions of individuals are often just too prone to errors and malice.

Once individuals can synthesize viruses, armed drones, atomic bombs and AIs in their cellars, there will be a myriad ways of things going terribly wrong (in addition to the myriads of things that can already go wrong).

Ladies and gentle, witness the justification of the dystopian future before you.

Here is my problem, or my main problem, with this line of thinking. America is founded upon the idea that individual liberties are basis for all other liberties, and while I can understand the reasoning that the national security apparatus finds the shifting sands of power from nation states to individuals a potential security threat, they have embraced this thought process without bringing it to the people in an upfront manner as should be properly done in a constitutional representative democracy. This model of thinking, at least in the USA, is a complete rewriting of what we consider our government should be, and a rewiting that is happening with no informing the people, and one that will most certainly have more unintended consequences than anyone can yet imagine.

I am certain of one thing, and that is the worst things will befall those who so eagerly trade liberty for security, at the hands of those who promise to protect.

I think stuff isn't being rewritten - people are starting to figure it out by themselves, at least those who understand the technologies we're talking about here.

Honestly, it doesn't matter what "idea" America was founded upon. The whole talk of "trading liberty for security" has become a religious dogma now, when originally it was meant only as an observation about a narrow group of cases. We will have to have more centralized security and more surveillance if we want to survive our technological growth. I'd much prefer to live in such "dystopia"[0] than in a country whose people got sick and died believing in the idea that individual liberties of a random dude with access to an advanced genome sequencing machine are basis for all other liberties.

[0] - personally I'm rooting for something closer to the United Federation of Planets.

"Honestly, it doesn't matter what "idea" America was founded upon."

On the contrary, I think it is of the utmost importance that America was founded by We The People and that if you completely undermine the mandate of government by the people as set in the preamble of the Constitution then you are essentially declaring American government illegitimate.

"We will have to have more centralized security and more surveillance if we want to survive our technological growth." ... "personally I'm rooting for something closer to the United Federation of Planets."

Do you really not see the danger of this? I understand the theoretical justifications globalists/universalists have, because they think the idea of national sovereignty is an old relic of the past, but I think such a viewpoint fails to take into account the primary issue: centralization is a weakness, not a strength. In just about every structure, especially one in which massive power flows, a centralized structure is much easier to subvert, manipulate, and control to more nefarious ends.

"I'd much prefer to live in such "dystopia""

That's your prerogative, and I'm not sure if you are an American or not, but I have personally sworn an oath to defend the Constitution from all enemies, foreign and domestic, and I'm not about to just give up on the Constitution, the rule of law, or the will of the people and their freedoms and liberties for purported security.

This is what makes America exceptional in an increasingly European post-colonial world.

founded by We The Slave Owners...

Thats such a rhetorically empty statement. No one claims it was perfect or by perfect people, but they certainly bested the British system! At least I don't have to swear allegiance to a Queen! The Constitution is my king.

I'd much prefer to live in such "dystopia"[0] than in a country whose people got sick and died believing in the idea that individual liberties of a random dude with access to an advanced genome sequencing machine are basis for all other liberties.

And I'd rather die on my feet that live on my knees.

As far as I'm concerned, freedom is it's own end and needs no further justification. I mean, to be free is to have agency, and to be subjugated is to be denied that agency. And from what I can see, it's our agency, our free will (or the illusion thereof), our freedom to make decisions, that fundamentally makes us human. Without that, I see no reason to live at all.

> As far as I'm concerned, freedom is it's own end and needs no further justification.

That's your opinion, you have a right to it. And it would be perfectly good thing if you were the only human in the universe. But I think you haven't simulated the evolution of a system where such thing was the primary value and there is more than one human present - where you can't have everyone having perfect freedom to do anything. Let's try and do it.

First, you start with humans who value their freedom to do anything. It means that I value my freedom of taking food you collected. You value your freedom to fight me back. The system is one of violence defining bounderies of freedoms. It's not a very productive system. Humans are smart, so we notice that if we mutually agreed to suspend our freedom of taking the resources of others (which we will now call "theft" or "robbery"), we can reduce our defense spending and put the work to satisfying other goals. It works well, but it's a fragile arrangement - the first person to defect and draw their sword gets the resources of the rest. So (skipping some stages) we figure out that we may codify the agreement to not steal/rob and outsource the enforcement (including violence) to a group of people that will get some of our resources as a reward. And hence, the rule of law is born, and everyone is happier and more productive.

Going through this process is what defines civilization. And I want to live in a civilization.

And I think you're making a lot of assumptions about what I believe. Nothing I believe contradicts the idea of civilization, as long as the basis of that civilization is voluntary participation, with the use of force reserved for defensive purposes.

And hence, the rule of law is born,

But so very much of what passes for "law" today is nothing of the sort. But my view of what constitutes a valid law is pretty much a reflection of what Bastiat had to say (minus the religious stuff):


Maybe one day we'll live in Scott Alexander's Archipelago[0], where you'd be free to move to whatever civilization had the rules you like the most, and if you don't like any, you will start a new one yourself. But we don't live in Archipelago, we live on planet Earth, and we have a lot of work in front of us to build the Archipelago - work that requires us to coordinate, and coordination requires suspending some of our freedoms.

[0] - http://slatestarcodex.com/2014/06/07/archipelago-and-atomic-...

and coordination requires suspending some of our freedoms.

I'm not sure I would agree with that. From my perspective, all coordination requires is voluntary collaboration and free exchange. After all, people can (and do) choose to do things for "the greater good" even when they don't have to.

Cooperation in its root is voluntary suspension of freedoms. I voluntary agree to not do Bad Thing X if you agree to not do Bad Thing X too, and we both reap the benefits. But in practice, coordination is very fragile, and that's why we invent devices for enforcing it - social norms and local enforcement works on small scale (few dozens of people); on a larger scale we usually end up with a government.

> Nothing I believe contradicts the idea of civilization, as long as the basis of that civilization is voluntary participation, with the use of force reserved for defensive purposes.

I was born here, I don't want to move and I don't want to pay taxes. What will your civilization do with me?

Nothing. Why would it, unless you commit some act of aggression against someone?

Well then, how will you finance the civilization, including the nessesary defensive force?

I'm not going to do it voluntarily.

Some people will do so voluntarily. If you don't, yay for you, you get to freeload. And the "necessary" defensive force is just what the members of the population are willing to fund.

Then at some point some other state arise that is more efficient at taxing, and conquers your state.

Obviously it's not your fault, but building unrealistic system 100% conforming to your values vs building realistic system that conforms 90% to them is interesting question.

I think it depends on whether the security apparatus is a central or decentralized one. Perhaps one would need to decentralize the decisions of individuals, but I can't think of a particular implementation of that idea.

"Private companies only change when they have to."

I think this is true for all institutions. Change need to be first enabled and then forced. This is because institution is not a solid thing, it's a while loop. A process that needs to feed itself to exist. So it has natural inertia to stay the same.

I think democracy is enabled by efficient taxation of businessmen. So you no longer need aristocracy as middlemen to collect taxes.

It's enforced by necessity of defense. You can motivate peasants to defend "their country". But you have to let the vote for it to feel theirs. This worked at an age when you needed lot's of fingers to pull lots of triggers. There was proof of concept: https://en.wikipedia.org/wiki/War_of_the_First_Coalition

Looks like weapons technology and general resentment against conscription is enabling whatever comes after democracy.

I've tried to understand what are you saying, but I didn't get it. Would you care explaining it in simpler terms?

Would you argue that our system is much more based on taxation than on decentralization of decision making? Isn't taxation a form of decentralization of decision making as you move the means to make decisions to a central pool? Also, why do you have to let people vote to feel what? What is WotFC a proof of concept for? How will weapon technology and resentment against conscription shape, what are possible scenarios you have in mind?

I think "decentralization of decision making" is a result, not a cause. I love it.

In geopolitical way of thinking, a state is always competing with other states. Not because we are bad people, but for the simple fact that states that can hold their own are likely to survive. Certain type of political "evolution".

To succeed in that competition you need armed forces. For that, you need manpower, equipment and supplies. All can be bought with money. So successful taxation is essential for any nation.

When traders and banks started to amass wealth at end of medieval period, any state that could tap into that flux of money had upper hand. But taxing individuals or sales actions or anything like that is more difficult than taxing nobles based on the land they hold. It helps a lot if those people have some sort of motivation to pay taxes. Concept of nation state provides such patriotic feelings. Now you are paying taxes for your people, not your feudal lord. Accounting and bureaucracy in general are also key elements.

French revolution established democracy and right after that the French levee en masse could defend the country against very big and powerful nations. Despite the facts that the french were short of money, had few trained troops and only little time. It showed that you could compensate with motivated and numerous troops. Imagine if you had democracy and money? This happened in the period where rifle had become more important in the battlefield than trained cavalry.

Possible scenarios? I think cryprocurrency will put traditional taxation in a binge. Governments need to tax what they can control, income and sales are going to be difficult. Taxation of energy seems easiest. Both persons and companies need energy. And it has some legitimacy with environmental concerns. Another big one is going to be information, it's difficult to lay cables without government knowing about it.

National identities don't seem to be important to people anymore. Conscription seems to become unneeded as well as unpopular. Bureaucracy is not going anywhere.

Political power seems to be shifting towards military-industrial big players. I don't think we will see feudalism. But maybe a modern version of powerful families of Venetian Republic. This time more with company allegiance than family ties.

Was that more understandable?


EDIT: I just would like to add that technological progress seems inevitable. But speed of technological development seems often biased. It's likely that current power structures pour R/D money on technologies that keep them in power. And it's completely possible that some unforeseen technology emerges and changes the picture totally.

I like Swedish arms production for this reason. For example they develop new anti-tank missiles to keep infantry relevant in the battlefield. Which in a way promotes democracy.

"The cost of destroying the world falls by the day"

Paraphrased, can't remember the source

Also, "the necessary IQ for destroying the world falls by the day".

May be true but not applicable to this story about a rail gun that is more dangerous to the person setting it up and firing it than any potential target of it.

The thing couldn't even shoot through two sides of a car door.

True, but note that this project can be done by any random teenager (closer to 12 than 18 years old) with no access to specialized materials or equipment. Aluminium and copper is around everywhere, and you can pry HV capacitors from off-the-shelf equipment (as a kid I used to get them from spent single-roll analog cameras). Instructions you can find on-line. In contrast, making a working gun at home (and more importantly, ammo!) is much more difficult (though still doable), requiring some specific chemicals and a lathe if you want to finish it in under a decade. Though the latter is changing as well, as the lathes are more precise, cheaper and easier to get than they used to be.

And this is still very low in the category of actual damage - close to the top I'd put a resourceful teenager halting a desalination plant or crashing the power grid in some country using only his laptop. Actually, I'm still a bit surprised it hasn't happened yet given the laughable state of infosec in the industries.

The point of the quote is - our technological advancements tend to raise the amount of damage a single person can do by using products of the system against the system itself. And this is a big problem, because while you can hope for some level of control over countries or even corporations, with 7 billion people on this planet, some accident is bound to occur eventually, and individuals hell-bent on destroying the world pop up by pure chance.

> note that this project can be done by any random teenager

This thing is optimistically as powerful as a handgun. Any random teenager with over $50K and two years of time to sink into this kind of project can get a gun.

A teenager with $50K can obtain a car and just run people over, too. That's both more likely and more effective.

> The point of the quote is - our technological advancements tend to raise the amount of damage a single person can do

Our technological advancements also tend to raise the amount of "the sky is falling" paranoia. When drones first started getting popular, I saw several articles about how terrorists were going to build smart bombs with GPS-guided drones. This is a legitimately plausible scenario. The question is whether someone with the resources to build a drone with sufficient range and carrying capacity to do real damage could do the same without drones, and the answer is most certainly yes.

New tech doesn't necessarily mean more danger, even if it means new types of danger.

$50k would be the retail cost. The guy got his for < $4k.

> Our technological advancements also tend to raise the amount of "the sky is falling" paranoia.

I've noticed that too. I don't want to sound paranoid about technology in general, and I'm not worried about terrorists doing their terrorist things. I'm worried what an average random individual could do, whether by accident or on purpose. Most of the popular dangers don't multiply the power of an individual enough. But biotech does.

> The guy got his for < $4k.

Thanks. I missed that. How did he manage to get these for 1/10th the cost? Still, I'm pretty sure a black-market handgun or a beater car can each be obtained for <$4k.

> Most of the popular dangers don't multiply the power of an individual enough. But biotech does.

I could see that. I'm not sure how much biotech is really going to be accessible, though. I think much of it will end up locked down (legally), and I suspect that the regulations will be fairly effective. There are already biological agents that people can harvest, but it's relatively uncommon.

> Thanks. I missed that. How did he manage to get these for 1/10th the cost? Still, I'm pretty sure a black-market handgun or a beater car can each be obtained for <$4k.

I don't know, but one of the way I used to source (much smaller) HV capacitors for free was disassembling flash modules from single-use cameras that were thrown away after film was extracted from it. Generally, there are ways. In my city there is an electronics market where you can source a lot of parts (some extracted from old devices) cheap. I haven't asked for how much they sell those big HV capacitors in Shenzhen yet, but I'm willing to bet it won't be anywhere near $800/pc.

> I'm not sure how much biotech is really going to be accessible, though. I think much of it will end up locked down (legally), and I suspect that the regulations will be fairly effective.

I don't know either; we'll find out in a decade. But I don't see it effectively locked down in the longer (10+ years) run, unless something slows down current wave of progress that is happening around biotech equipment. Like with 3D printers, a lot of things you needed shit ton of money for can now be done with DIY equipment in a garage. This gave rise to community biolabs (biohackerspaces).

> There are already biological agents that people can harvest, but it's relatively uncommon.

True. I ascribe this to people generally not being evil or having murderous instincts. What worries me more are accidents and incentives-induced-stupidity. As an example of the latter, the most common bioattack people are doing right now is coming to work sick. It's actually mind-blowing that so many companies (outside IT) force people directly or indirectly to come in sick, even though it results in other employees getting infected and overall productivity in the company taking a hit.

   " individuals hell-bent on destroying the world "
Ha, on Criminal Minds my favorite quote is from a scene where it was observed that a teenaged boy profiled as a sociopath. The boss replied "Every teenaged boy profiles as a sociopath; you know that!"


I'll start worrying when the actual amount of danger exceeds what a rural teenager can do with access to a farm supply store and $20.


Slam-fire shotgun can be built, in a day and in total secrecy, by a 12 year old with some loose change in any modestly equipped garage. It is extremely easy to conceal and carry, you can reach 30+ shots per minute with little training and, sadly, ammunition for it is probably less time (read: resource) consuming to acquire in many countries than the knowledge of electrical engineering sufficient to build a working railgun of that scale.

Never heard of slam-fire shotguns before. I'll look into it. As a kid I had seen designs for railguns though.

I disagree that the shotgun would be easier because of ammo issue. It may be as you say in the US of A, but in Europe it's not that easy to get your hands on live rounds. Also, I doubt people often sell ammo to a 12 year old - so in order to get it, you'd have to interact with a grownup. Railguns are easier; your parents will never know what you're building even if you're spending your lunch money on high voltage capacitors.

Didnt he say he spent 50,000 on those caps?

No, he said that would have been the retail price. He bought them for much less. In other places, he mentioned that his total cost for the project was about $4,000.


Is the oldest source that I remember (from page 37).


> Moore’s Law of Mad Science: Every eighteen months, the minimum IQ necessary to destroy the world drops by one point.

Can't there also be a myriad of things that can go right?

Has there ever been something that has gone right?

Literally the entire human race, averaged over the last 4000 years.

Slavery, genocide, and tyranny are a fact of life for many people in the world today. We haven't gotten it right yet.

All done under rules of law.

Everything that can go right, will go right. -- Murphy was a pessimist.

Eventually : )

Or to quote Uncle Ben > "With Great power comes great responsibility" ?

lol @ the idea of a system that relies on responsibility of individual free will for general public safety. "Sure! Of course you can have firearms! Just be responsible and don't shoot anyone with it!"

Has worked mostly OKish here for a few generations it seems.

Also remember you cannot trade liberty for security.

Well, you can; Franklin's quote is not an iron law of politics. Every little bit of product, agricultural or environmental safety is an infringement of "liberty" that improves safety. "Freedom" is not an infinitely fungible gas, but must be considered in terms of specific freedoms to do specific things.

I'm quite happy to give up the freedom to run, say, a toxic waste dump in my garden to prevent my neighbour from having the same freedom.

In what year would you consider the US to first be a free country?

Mostly okish minus tens of thousands of unnecessary and/or accidental deaths and little to no actual benefit (like idk, mass shootings or terrorist attacks prevented). IIRC the right to bear arms was intended so that the people can overthrow the government if need be; small chance of that now, with the military and police forces as advanced and militarised as they are now. /rant

I am not american nor a gun owner but man, this is a very... unclever approach. I could put here quotes about people who give up a bit of freedom for a bit more security deserve neither, but I presume that's old school talk for you too. Except it isn't.

Guns don't kill people, people kill people. We are not yet in the age of some automated gun turrets. If you want to blame guns, then blame all knives, baseball bats, axes and whatnot. All shall be banned, no? I say yes, I see no difference between being shot and stabbed to death, for both you need a clear intent, but accedents can (and do) happen.

Seriously, how hard is to understand that weapons are not bought only for attack, but also for self-defense, ALSO for sport/fun, as collectibles etc. In fact, it takes a extremely dull character who needs to commit a crime with a weapon and goes to store to get registered for one. I mean, seriously, this is what you are saying? Because this isn't ahppening. Ban guns, and you'll severely restrict common citizen's access to them, but not so much criminal's one. In fact, i would expect illegal arms trafficking to skyrocket. War on drugs all over again.

There should be a check (of rules/laws knowledge, mental capability, clean criminal record etc.) before selling a gun. Guns for civilians shouldn't be full automatic either. But that's it. Rest is about living in freedom, or in a system that doesn't trust its own citizens and needs to control them. Just look at any news how power-greedy politicians are.

Who are you to tell other people they should abandon their hobbies ie of practise shooting, just because you feel that their real power to overthrow their government is "small"? You would be surprised how untrue this really is if whole nation would stood up to its government. But without guns, of course they wouldn't stand a chance

> Guns don't kill people, people kill people.

The whole rationale behind the "guns will protect our liberty" movement is that it is much easier to kill people with guns than with baseball bats and knives. It's just that in practice the people being killed relatively quickly and effortlessly with guns are real civilians and not hypothetical fascist stormtroopers.

> IIRC the right to bear arms was intended so that the people can overthrow the government if need be; small chance of that now, with the military and police forces as advanced and militarised as they are now.

However it seems that most low tech insurgencies fighting against the advanced conventional militaries of the West always seem to win, from Vietnam right up to Afghanistan / Iraq.

Because they gain a greater advantage by going guerilla than they lose by having inferior tech and training. You can't hold an unwilling populace in order for long - you either have to convince them to accept your rule or get ready to ruthlessly massacre them. The West sucks at the first and doesn't want to do the second.

> However it seems that most low tech insurgencies fighting against the advanced conventional militaries of the West always seem to win, from Vietnam right up to Afghanistan / Iraq.

But it didn't really work during the US Civil War.

I'm only making this point in reference to conflicts that involve insurgencies.

>little to no actual benefit (like idk, mass shootings or terrorist attacks prevented).

How can you possibly judge that? For all you know, having 300 million guns in America is keeping the earth's magnetosphere intact through some weird quantum effect. It's highly unlikely, but you have no idea what the actual benefit of the 2nd amendment is because there is no possible way to empirically determine what the past would have been like without it.

You can compare to other countries without that right, or to just within regions in the same country that have no guns vs regions that do. That's how you would determine the benefits of the 2nd amendment with data.

This is not a difficult problem.

The right to bear arms was never for the purposes of overthrowing a government.

It was given in order to establish militias, which the government can use to prevent insurrections and invasions, per section 8 of the US constitution.

No government allows its citizens the right to overthrow it. I have no idea why people think that? Do you?

"I have no idea why people think that? Do you?"

Because they had, in fact, just overthrown an oppressive government. I have no idea why you think the founders did not consider that potential outcome. Jefferson even said "God forbid we should ever be twenty years without such a rebellion".

Can you think of another example of the right of the militia to bear arms ever being codified, anywhere in the world? Why would it need to be?

The right is specifically stated as being one of the people's rights. The militia is a reason, not the subject.

If the First Amendment had read "A well educated Legislature, being necessary to the security of a free State, the right of the people to keep and read Books, shall not be infringed" would you argue that only legislators had the right to keep and read books? No, you would not. Nor would anyone else, because that would be a nonsensical interpretation.

"God forbid we should ever be twenty years without such a rebellion. The people cannot be all, and always, well informed. The part which is wrong will be discontented, in proportion to the importance of the facts they misconceive.

If they remain quiet under such misconceptions, it is lethargy, the forerunner of death to the public liberty. … What country before ever existed a century and half without a rebellion? And what country can preserve its liberties if their rulers are not warned from time to time that their people preserve the spirit of resistance?

Let them take arms. The remedy is to set them right as to facts, pardon and pacify them. What signify a few lives lost in a century or two? The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants. It is its natural manure."

-Thomas Jefferson, Letter to William Stephens Smith (13 November 1787)

That's one individual's personal opinion.

The official US government question was already answered the 1860's. Many people had the mistaken idea that government allowed them the right to rebel against it. About 600,000 people found out the hard way that it was never their right.

People need to get their egos in check, because government always wins.

>Also remember you cannot trade liberty for security.

Probably worth mentioning the quote from Ben Franklin so often paraphrased out of context was, actually, an argument for taxation and federal military power (specifically to fund defense of the frontier against Native Americans), not a warning against it.


What about people being conscripted in WW2 (loss of liberty) to defeat the Nazis (increase in security)?

It would be very interesting to see what could be done with a much smaller projectile. I'd imagine there's a sweet spot for maximum energy transfer and that 22grams is somewhere above that.

Presumably, you would like the reverse EMF from the projectile moving through the magnetic field to provide the majority of the load voltage in the circuit and be large enough that the current continues at over half its max until the projectile makes it out of the barrel.

If the projectile is too large, then you will get all of the energy out of the capacitors, but the slower motion will result in a lower back EMF, and consequently most of the energy will be dissipated resistively, probably mostly in the arc between the rails and the projectile.

If the projectile is too small, then almost all of the power in the circuit will be reactive, but the projectile will leave the barrel while the capacitors are still mostly charged.

Calculating this is somewhat complicated by the fact that the voltage across the projectile will be highest as it leaves the barrel, because that's when it's cutting the maximum amount of magnetic flux per millisecond; but that's exactly the point where the voltage across the capacitors is lowest, since that's when they stop discharging.

Maybe you could remedy this problem by using a flywheel-driven homopolar motor instead of capacitors. Failing that, probably the best you can do is discharging the capacitors to something like half voltage, transferring three fourths of their energy into the arc and the projectile.

Your two arcs, assuming a length on the order of millimeters, are going to suck up minimally 50 or so of your volts, which is one reason to use higher voltage — so that the relatively fixed voltage drop across the arcs doesn't hurt efficiency so badly.

https://en.wikipedia.org/wiki/Tesla_%28unit%29 suggests that the maximum field you can reasonably expect to achieve across the rails is on the order of 500 milliteslas. If you were going to keep using 400 volts, discharged down to 200 at the time of exit, then the optimum would be to have a back EMF at 500 milliteslas of about 150 volts at whatever the muzzle velocity is. 150V / (500 mT * 20mm) = 15 km/s, about Mach 45 and about twice the speed of, say, the International Space Station.

Okay, so if we have, say, 15kJ of projectile energy at 15 km/s, how massive is the projectile? 15 kJ / ((15 km/s)²/2) = 130 mg. One difficulty with this is that small, light projectiles slow down more from air resistance, which is significant when you're talking about flying fast enough to suffer ablative erosion from turning the air in front of your projectile into plasma.

So, you're right. 22 grams means that the capacitors finish discharging far too early, so almost all the energy would be dissipated in the resistance of the arc. Except actually I think most of it ends up in the flapping cables, which weigh a lot more than 22 grams. You could probably get a noticeable improvement in the penetration just by tying the cables to boards so they can't flap around and generate so much back-EMF of their own. (They'll still generate a significant amount due to self-inductance, which you can reduce but not eliminate by tying the opposite-direction cables very closely together.)

But wait! What if the magnetic field is weaker? Achieving 500 milliteslas is pretty hard, after all. MRI machines have a field on the order of a tesla, which creates hazards of its own, though that's mostly due to the field being distributed over a large volume. If it's only 50 mT, then you need the projectile to be going ten times as fast to build up that same 150 volts of back-EMF: 150 km/s. And that, in turn, means that your sweet-spot weight goes from 130 mg to about 40 mg.

You could improve the situation for massive projectiles, at the expense of arc losses, by using a lower voltage and higher capacitance. And of course a stronger magnetic field would help too, but I don't think that's very practical.

I don't know, maybe I've missed something in my calculations here. You'd think that barrel length would enter into it somewhere, for example.

I wonder if a small railgun could be made portable for infantry, and how much power per shoot it would be. Because the home made ones don't seem that much powerful in term of muzzle energy.

Well they're being used by the Navy now to shoot down missiles, as far as I know. I think the tradeoffs are that they are super heavy and require a lot of energy but they can accelerate projectiles extremely fast. Very useful if you're trying to shoot down something that's also moving obscenely fast but not so useful if you just want to poke a hole in a living target running at 10 miles an hour.

Capacitors have really bad energy per volume figures. People underestimate how much energy chemical stuff has--gasoline, batteries, etc.

The only thing that looked to me like it couldn't be made smaller/lighter was that capacitor bank. Are there smaller lighter capacitors that can produce the same?

Reminds me of Neal Stephenson's novel "The Big U", where (among other plots) students build a railgun.

I parsed the title as:

> Most powerful mobile railgun was built by a non-government (i.e. this is the most powerful mobile railgun)

when in reality it probably is:

> Most powerful mobile railgun that was built by a non-government (i.e. there are more powerful mobile railguns)

Is the title ambiguous or is it just me?

The way it's written now (The most powerful mobile electromagnetic railgun built by a non-government) seems pretty non-ambiguous in implying that more powerful mobile railguns have been built by governments.

If you want to get technical (and who doesn't?) the giant railguns mounted on navy warships are mobile. They're definitely more powerful than the device in the article.

I suspect that government defense contractors have repeatedly built man-portable prototypes that just don't measure up favorably against the .50-cal rifle. The government then mothballs the project again, until better electronics technology comes along. It also seems obvious that anything that did measure up would be classified as a state secret, so we wouldn't necessarily even know about it.

So the implication I got is that government-built devices are purposefully excluded, because we have no way of really knowing how powerful the most powerful government-built mobile railgun is.

I see, thanks. For me it can read either way (and the wrong meaning actually comes to mind first).

>The current flows in a C-shape through the device. This C-shape produces outward force in all directions, like water flowing through a bent rubber hose.

One really shouldn't expect any measurable force from this effect. I don't claim that this effect doesn't exist, but electron mass is really small and electrons usually travel really slowly in metals (mean velocity, not to be confused with Fermi-velocity, which is usually quite large), even at relatively large currents. I can make a simple calculation for the author's construction if anyone's interested.

One can build guns based on induction and Lorentz-force but I think using the electrons' inertia is completely unfeasible.

I imagine that someone is going to have a visit by the FBI.

That or a job offer.

Is it illegal in the US to build your own railgun? I know that in Germany there is a limit on the Joules you can put in a projectile without a licence, I think something like 8 Joules. This gun would violate that, I guess.

Applied strictly, this probably means that some Olympic sports require a license (hammer throw, discus throw, shot put and javelin)

And of course also Icehockey,Football and a lot more. The german law is bit more specific about it (the exact amount of Joule is 7.5) http://www.dsb.de/media/PDF/Recht/Waffenrecht/Verwaltungsvor... e.g. the weapon/weaponlikethingy must have a muzzle. Also the Intention of usage is considered, so if you produce a hammer with the sole purpose to throw it at me, if may offend German law.

8 Joules is a really small amount of energy. I wouldn't be surprised if an average healthy child could put that much energy into a ball by kicking it. A quick back-of-envelope calculation says a 0.45kg ball (FIFA standard ball) traveling at 6m/s (~13MPH) has more than 8 Joules of energy.

Then again, a ball is an awfully heavy and big projectile.

I'm pretty sure carrying a javelin around in Germany gets you in trouble. The police can get you in trouble for carrying around pocket knives if the blade is too long or locking.

My brother used to carry gladius (in a pouch, on his back, to and from training). No cop stopped him to ask about it, ever.

Just like cops rarely stop you if you're cycling without lights after dark. If they have a reason not to like you they can still use that to slap a fine on you.

However, I'm pretty sure if he'd started waving it at people in the street they'd have become quite a bit less lenient about the fact he was carrying a weapon around.

In the reddit thread [1] the creator mentions many times he asked the BATF it what he was doing was OK, and they never replied. He's confident there is no law against electromagnetic weapons.

He also mentions he's an engineer and has designed/built weapons that have actually been used lethally, so I get the feeling he knows what's he's talking about, professionally.

[1] https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_gian...

Judging from the size of his projectiles, the bore of his device is almost certainly over 12.7mm in "diameter" (it's square, not round, but it looks to be 0.5" by 1", and I'm not about to leave the hairsplitting to a federal bureau). Classification of a "destructive device" doesn't really care what type of propellant is used. I think it's pretty clear what he has here would be considered a "destructive device". It'll depend on his state whether or not it's legal for him to have.


It would put interesting spin on the second amendment fights though.

There was floating on internet a very old post about how to make a railgun, made by a Brazillian guy... he DID got a job offer, but the superiors of those that tried to hire him shut it down because he was Brazillian (he was a Brazillian living in US, he wasn't allowed to legally make weapons for the government, at least for whoever tried to hire him, I don't remember anymore what department it was)

This or any extremist group ...

Metal Gear?!

Kind of amazing you can build this and not get a visit by any government entity.

Of course right now it is far less powerful that any shotgun/rifle you can buy without any background check at a gun show.

We are more than a bit insane about weapons in this country.

We are more than a bit insane about weapons in this country.

How so? We purport to be a "free country" and part of that entails the right to own weapons. Just because some people spazz out with irrational fear every time the hear the word "gun" doesn't mean that the rest of us have a problem. Consider that, by far, the vast majority of firearms owned in the US will never be used in the commission of a crime. I don't have the numbers in front of me, but somebody worked out the math and based on existing statistical trends, it's a minuscule percentage of firearms that will ever be used to commit a crime.

It's not a dangerous weapon for any practical purpose, because it's weak, single-shot and not portable. You wouldn't be able to say, rob a convenience store with it. Government has more dangerous things to bother with.

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