3D printed, portable railgun fires slugs at 560mph


#1

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#2

Not practical? That’s what they said about the Gyrojet pistol…


#3

Parts of the case are 3D printed. That’s not quite the same as a 3D-printed railgun (which I’d still like to see)


#4

Somebody needs to introduce this guy to The Slow Mo Guys


#5

560mph is approximately the velocity of a BB gun. Whatever is causing the projectiles to vaporize, it’s certainly not from the impact with the target.


#6

Yes, but the energy delivered by the shot is proportional to the weight of the bullet, not just the speed.

A BB pellet apparently weighs 0.2 g, so at 560mph, or 250 m/s, it will hit a target with just 6.25 joules.

I can’t find the weight of these bullets, but this thing claims to shoot with 1,800 joules. Even if we assume only 50% efficiency, that’s still well over 100 times the energy that was delivered by a BB pellet.

Edit: the bullets shown here could easily be 2 or 3 grams, so that matches the calculation above of 100-150x the energy.


#7

Note that it’s the graphite projectile that vapourized, not the aluminum-coated tungsten.

The aluminum ones are 4.3g. Here, you can see him hitting a cantaloupe with one, point blank (the shot energy is showing as 1372J). Doesn’t even go all the way through the cantaloupe. Neat, but not as terrifying as I was expecting.


#8

560 mph is a little over 800 fps. That is the speed of a fairly slow handgun round such as a 45 ACP (the slower ones). A 45 ACP round is about 230 grains which is 14 grams.
This has less power than a common handgun.


#9

What size is the projectile? 560mph is not impressive compared to a firearm - but it is a neat start.

ETA - Actually - depends on the size of the projectile. Depending on size it could be pretty impressive.

IIRC the rather weak 5.56mm is about 1700 Joules of energy, so even though it is slower, it is an impressive amount of energy.

He might want to invest in some AR500 hardened steel plates if he gets things spitting out even faster.


#10

The most popular hunting rifle cartridge is the 30-06 Springfield and its energy is around 3300 joules at 100 yards. The slugs most certainly do not vaporize on contact with steel… (edit: the projectile that vaporized was apparently made of graphite)

There are lots of muzzle energy calculators online, here’s one with some presets for common rifles/ammo.
https://billstclair.com/energy.html


#11

I don’t think anyone suggested otherwise, but the fact that we’re comparing it to a handgun at all is impressive for a DIY project.


#12

98% the speed of light or GTFO!


#13

I feel like “3D printed” and “portable” are steps backward in railgun development. We should be aiming more for “cold forged in the foundries of Mars” and “mech-mounted.”

Worth a punt on kickstarter?


#14

Vaporising graphite is somewhat unlikely. Temperature of combustion is about 600C, sublimation point is 3900K. Heat of fusion is around 117kJ/g atom, so this thing could not even vaporise a gramme.

Do not remove a graphite crucible from a hydrogen furnace until it has thoroughly cooled, by the way. Unless you really want to - in which case ventilate well.


#15

I’m sure by “vapourized” he (the railgun guy) actually meant “smashed into a million tiny pieces” as opposed to “actually turned into a vapour”.


#16

I’m actually a bit worried that if he is that ignorant of basic physics/chemistry that he doesn’t know the difference between vapourised and pulverised, he’s not the best person to be fooling around with something that stores 3kJ.

(Mind you, he also doesn’t have those capacitors inside a suitable enclosure. If one of them does manage to self-discharge due to local breakthrough/sparkover, the consequences could be serious. In the days when I was developing rapid discharge stuff, capacitors like that went in a suitable steel or glass fibre reinforced enclosure. I still preferred lots of small capacitors to a few large ones to reduce the risk.)


#17

That’s making a big assumption, though. He may very well know the difference, and just chose to use a word that, to many lay people, means the same thing.


#18

You mean he’s a politician?

I repeat my point; a real engineer or physicist involved in…let’s call it radical kinetics…would argue, loudly, with anybody who didn’t know the difference. Just like steam engineers and physics teachers despair of people who don’t know the difference between condensing water vapour (visible) and steam (invisible). And I personally would not want to be around someone handling that much power if I suspected they didn’t quite know what they were doing. I’ve been involved in the design of safety interlocks and protective enclosures for stuff with peak power in the MW range; it is not trivial (we had safety videos of incorrectly wired plugs exploding and spraying molten brass around, for instance.)
And I’m posting this because I have a conscience and I don’t like the idea of somebody who doesn’t really understand what can happen thinking “I’ll make one of those” and ending up blinded.


#19

Quite possible that’s a feature and not a bug.


#20

So he can get ricochets and kill innocent bystanders?

Kevlar possibly best, softwood at a pinch ( start with balsa layer, end up with oak.)