Railgun

[Energy84]

Has anyone tried making one of these? I'd like to build my own, but I need to learn a few fundamentals about magnetic fields, formulas etc... I'd like to build a gun with about a .50 inch barrel and loots of power (of course). I need to know stuff like what material to make the barrel from? how many winds of wire and what gauge? how much current/voltage is required?
A buddy of mine brought up the idea of building a railgun and now I'm obcessed. He told me that the amount of winds is directly related to the barrel length. He also had an idea about converting a paintball gun into a railgun and letting the air pressure get the projectile moving. Would this really be necessary? Oh, and is there a specific metal that the projectile would need to be made of for optimum performance?
Thanks for the help everybody!

[PYRO500]

reailgins don't use coils of wire, if you needhelp with one visit www.powerlabs.org (http://www.powerlabs.org) and ask at hteir forums.

[Ctrl_C]

you are correct, railguns do not use coil. they use charged rails to create a magnetic field. the hardest part about a railgun is finding a pulse capacitor with high voltage and amperage. search for 'gauss' on http://www.slashdot.org

there was an article there recently on a similar concept but some of the discussion talks about railguns.

[Mr Cool]

Railguns can use coils - two rows of coils, one above and one below the rails, so that the field lines go straight down through the rails and armature (bullet). You have to have the field in the right direction though, or it will have a negative effect on performance.
Every time this has been discussed on the Forum while I've been here, it has been decided that if you want something that works for under a few £100, make a conventional coil gun, not a rail gun.

[PYRO500]

yes you can have electromagnets in a railgun to increase efficiency a bit but the militayry can only get around 5% so don't expect to get any higher, coil guns on the other hand are MUCH simpler and require MUCH less energy and can be relitively powerful, coilguns are alsocalled gauss guns fyi, the single coil ones are simple but when you get mucltiple coils things get harry, the advantage to gauss guns is thet you can use electrolytics on them.

[xoo1246]

Don't expect too much...

[Tyler_Durden]

http://scitoys.com

Some cool stuff there. I think there is somethin on a simple toy railgun.

[Ctrl_C]

interesting enough i borrowed (read: stole) some neodynium magnets and some steel ball bearings from physics today and made a simple gauss gun. it involves taping the magnets 2.5in away from each other on a ruler with a groove in it, putting 2 ball bearings in front of each and letting one go at the end with no ball bearings on the magnet. the 1st magnet attracts it, makes it hit, transfers the kinetic energy through the magnet and one of the 2 balls places there and to the other of the 2 balls. this said ball then gains acceleration due to the attraction by the 2nd magnet and so on. you can get a respectable speed out of 10 magnets or so.

heres a diagram where
0=ball
x=magnet
-= nothing/ruler


--0----x00----x00----x00----x00---

[Energy84]

Seems I got the terminology mixed up. I meant coil gun (hence the windings). But now that I've looked into it a little harder, it's hardly worth all the work involved. :(
Ctrl_C, I found this link last night http://scitoys.com/scitoys/scitoys/magnets/gauss.html that shows pictures of the simple gauss gun you just described.

[TariqMujahid]

Railguns...i've thought about making one of these. However, don't expect to match the Department of Defense's railgun, that shoots 6 km/sec.
Just think: a stungun can seriously injure someone, and it uses only a 9V battery. Why is this? Because of the capacitors. So, if you have a large capacitor bank (maybe a few hundred capacitors), you can perhaps get decent results.
For the materials of the rails, try using Copper or Silver...Iron won't do it. Same thing applies for the Armature, it must be non-ferrous.
An idea for shooting the armature is this: Do not simply insert it, and then turn on the power. Try using a pneumatic device to shoot the armature in, and then the railgun does its work. The advantage of this is: it helps to prevent overheating, which can weld the armature to the rails and short out the gun.
The magnetic fields on a railgun tend to push the 2 rails apart. So you will need a strong support frame that will hold the two rails together.
The 2 rails MUST be parallel to each other.
I had an idea for a railgun that would have 2 sets of rails, one going horizontally and the other vertically. When the armature passed through, it would complete 2 circuits at the same time. The advantage of this, is i'd have 2 capacitor banks; therefore it would charge up in half the time, while still using the same amount of electricity.
Railguns give off a lot of electromagnetic interference when they are fired, keep that in mind.
<a href="http://www.railgun.org" target="_blank">www.railgun.org</a> These guys are 2 students at MIT who are building their own railgun. I've asked one of them, Mouser, a few questions. They know a lot about the subject, send em an e-mail maybe.

[Ctrl_C]

hmm your pneumatic idea is a good one, but it would be difficult. first of all, the projectile would be pretty heavy. if you know anything about paintball guns, you know paintballs have a very short curving trajectory. this would be more evident with a heavy projectile being launched from something similar to (if not) a paintball gun. also, you would probably have to use a projectile slightly smaller than the barrel and use a pece of cloth or something as wadding to keep the pressure from escaping around the ball.

[Mr Cool]

The (pneumatic) pre-injector is not only a good idea, it's practically essential! Without one it's very hard to stop the armateur from welding.

[RTC]

What are military/industrial rail gun's made/used for?

[kingspaz]

i beleive they are used for testing pretty much. i also beleive they are (where?) part of the the star wars projects which involve various 'space age' technology such as chemical lasers mounted on aircraft. the project was originally made to find a way to defeat ICBM's.

[TariqMujahid]

The armature of a railgun must conduct electricity, but cannot be Iron. Therefore, a paintball would not work. It would just sit there. The purpose of the armature is to close the circuit between the 2 rails. The magnetic field that is created tries to expand itself, and therefore moves the armature up the rail. That's also why it pushes the two rails apart... So, having a wadded projectile simply will not work.
The Armature will have to fit snuggly in the pneumatic insertion device. I got most of this information from <a href="http://www.railgun.org" target="_blank">www.railgun.org</a> and searching online, so just look what they have. They have pretty good formulas for this stuff.

<small>[ March 16, 2002, 10:51 PM: Message edited by: TariqMujahid ]</small>

[Anthony]

I remain adamant that a personal raigun will never be more practical than a conventional firearm or even compressed gas power weapon. Until small, portable fusion generators are created.

Stunguns don't cause injury/pain because of the energy contained in the discharge, it uses the power of your own muscles to do that, it simply controls them. The amount of energy required to stop your heart is very small, considerably less than that contained within a 9v PP3 battery. The reason it works is because of the extremely efficient delivery method (if applied to the correct area of the body). Although again, its your own heart muscles which actually stop your heart, or make it fiblerate.

There are many very high energy density batteries available at the moment that would probably have enough stored energy to give you several rail gun shots that possesed energy equal to that of a firearm round. But the problem with these high energy density batteries is that they just can't handle high discharge rates so would take a long time to recharge your cap bank for a follow up shot. Forget double-tap...

It's much the same thing that prevents electric cars from catching on, basically that you get a lot more energy stored in small amount of chemical compound that can be released instantly. It might be less efficient but you're prepared to eat the loss because of its great advantage.

[TariqMujahid]

No, of course a railgun is not practical; that's a good point Anthony brought up. If you're trying to make a railgun as a substitute for a paintball gun, that will be very difficult. It takes a long long time for them to recharge their capacitor bank, and that's the reason you don't see them on fighter planes or soldiers armed with them. They need weapons with a high rate of fire, and shooting a shot; waiting a minute; and firing another just won't cut it. Railguns, atleast homemade ones, are only good for hobbyists. Similarly, you wouldn't take your homemade coil gun on a guerilla attack. But my idea, with the 4 rails would effectively cut the recharge rate in half. It's essentially 2 railguns firing the same armature. Therefore, it would have 2 separate energy sources...

[PYRO500]

Actually you'll get better efficency if you stick to 2 rails, if you want more contact surface area then a co-axial rail gun might be what you are looking for.

Today I finally got some parts for my rail gun. They are two silver plated copper bus bars, and 3 4,200V capacitors.

The bus bars are 3 feet 3 inches long and 2 inches wide, they are 3/16 of an inch thick. The capacitors I have are all rated for 4,200V and their capacitance that was measured at the factory is stamped on them, there are 2 298UF caps and a 297UF cap. The total energy these capacitors can store is about 7,876 Joules, witch 30 is considered lethal and 360 or so are avalable at a hospital through their defibulation machine.

I plan on using lexan for the rail gun body beacuse it's much more simple to cut than garrolite composite such as used on Sam Barros' page.

What I have to do now is cut the bus bars to the right lenghts and hook up all the cap's in paralell. then once there paralelled I can discharge them through a resistor and watch them on an osciliscope and try to find out how fast they'll discharge in my rail gun app so I can calculate the lenght of the rails correcly.

If you want to see pictures of the capacitor bank I'm building go to this link: <a href="http://pub13.bravenet.com/photocenter/album.php?album=3422&usernum=1081592780" target="_blank">http://pub13.bravenet.com/photocenter/album.php?album=3422&usernum=1081592780</a>

I have some pictures of the bank and bus bars there.

<small>[ October 13, 2002, 12:42 AM: Message edited by: PYRO500 ]</small>

[the resourceless reaperman]

Remember you don't need to use conductive material for guiding the projectile wihile it's still being fired. You could just use a wooden rail or a plastic one. Allthough the plastic might not withstand the heat caused by friction it will be more moisture resistant.

Also why have more that two rails for conduction? since you only need + and - it seems pointless to add more potentially damageable (is that english?) parts.

And what precautions are you going to take to make sure your expensive capacitors won't blow up?

The projectile you want ot use doesn't have to be solid copper (or whatever conductive stuff is used here)it can be something heavier with a conductive layer.

PS. does someone know/have any links about how to make a homopole generator?

<small>[ October 15, 2002, 09:59 AM: Message edited by: the resourceless reaperman ]</small>

[Boob Raider]

Pyro .... here's something I wanted to try .... but I don't have good charge dump caps. Anyways see if you can try this ... take really thick insulated (PVC insulated 14 gauge) Cu wire and wind say 5 turns on a Non-Ferro Magnetic rod (a brass screw). Then have only the 2 ends of the coil make contact with the rails (keep in mind the polarity of the coiled armature). I am suspecting a slug with a winding to be more efficient and faster compared to a standard slug. I have other coil windings to try but I'll wait till I get mine tunning.

[PYRO500]

I am only planning of using two rails like a normal railgun. I was only pointing out flaws with the 4 rail design.

For the railgun to have any kind of efficency the armature must make contact with the rails for the duration of the pulse. I have yet to determine the pulse so I can't calculate how long my rails need to be yet. I will do that when I get all my capacitors hooked up and working and calculate the ESR and ESL.

I'm not sure what exactly you ment about that conductive coating but I do know that if you use a metal strip behind a non conducting slug you will get a plasma armature rail gun and get higher speeds since your projectile is alot lighter.

As far as plasma armatures go I don't think I'll be using one due to the high pressures involved and the materials I'd need to use. It isn't that I can't afford G-9 Garrolite like Sam Barros, It's just that I lack the CNC waterjet cutter and such tools to cut the tough stuff. I plan on using Lexan or polycarbonate plastic for the gun.

I think the idea with the brass slug wound with a coil would decrease efficency beacuse it would raise inductance in the circuit and cause the capacitors to discharge alot slower decreasing the maximum amperage delivered to the rails.

[the resourceless reaperman]

that's why I asked about the homopole generator, it can create enormous amperages and discharge very quickly without being damaged.

PS. check <a href="http://www.geocities.com/thatsmeagain2000" target="_blank">www.geocities.com/thatsmeagain2000</a> if you still want to know what I meant by a metal coating.

[Positive Electron]

a close friend of mine made a small version with wooden rails that contained small amounts of mercury. he used wooden barriers to keep them from contacting and it worked pretty good. he had 6 7000v caps from his dad (a laser physics engineer) and he charged with 8 die hard batteries :)

one of the military guns used 14000 car batteries and had 2 35 foot long aluminum rails, and shot 22 million fps. the whole gun assembly took up 2 large warehouses, and they tipped a tank sideways with it, but the rails would destroy themselves after every shot, so they discontinued the project.

[Anthony]

Have you got a reference for that 22,000,000 fps figure?

[Marvin]

reaperman, homopolar generator creates very high currents at tiny voltages, the power therefore isnt useful. The only people still interested in them are the mixture of snakeoil salesmen and physics incompetents that still bilieve in free energy.

Somehow I think a coilgun whose magnets were coresonent with the accelerating projectile would be extremly efficient using superconducting windings. I wonder if this has been tried.

Edit, played around with some math.

22million fps is 2.2% of the speed of light.
That works out at about 50 tons of TNT per gram of armature.
Assuming the car batteries dumped the energy completely into the gun, with 5% conversion, would make the armature about 7.5mg.
I get the feeling at this power to armature ratio it would vapourise in the gun.
Anyone care to doublecheck these numbers?

<small>[ October 16, 2002, 09:41 PM: Message edited by: Marvin ]</small>

[firebreether]

No way it could do anywhere near 22,000,000 fps. I thought the record for a projectile was Sandia's rail gun, launching a .1 gram projectile to 16,000 m/s. Which is huge, considering bullets are around 1,000 m/s top speed rough estimate.

[the resourceless reaperman]

doesn't friction in the air melt the projectile?

[firebreether]

yes, going at high speed, aerodynamic heating will be high. But I'm concerned with this, if you choose to use a plasma armature, wouldn't it melt the rails and the prohectile in short order, i mean at the currents needed to produce high energy shots, depending on the voltage used, the plasma will be hot, and dense, and melterific.

[AfroFukinPyro]

Some friends of mine just made a coil gun (which as has been stated is different than a rail gun). This was just an experimental prototype, and although it was cool it was extreamy inefficient. The gun could shoot a screw about 3 meters, which is obviosly not even as powerful as the human finger, and the coil gun must be carried around. It would be very hard to build a compact, powerfull coil gun, and I'm sure if your seriose a rail gun is the way to go.

[Ctrl_C]

I was just thinking, what would happen if you shot a projectile from a railgun into another railgun set to discharge when the projectile entered it. kind of a series of railguns. could you achieve higher velocities? also, when they quote these figures, are they at sea level, vacuum, or other?

[PYRO500]

I think a homopolar generator will be far too low in voltage to supply the power a railgun needs. As far as I know HPG's need very good low friction brushes to work. IIRC I've seen some that use liquid mercury as the contact. If you were to make a generator & flywheel to run one of these directly you'd need a compulsator or a compensated alternator. Compulsators are kind of hard to describe but basicly they are like a generator that can supply huge currents at fairly high voltages to whatever their output is hooked up to, they can be made pretty efficient and power something like a railgun with a signifigantly heavy flywheel attached.

The only problem with a compulsator is that there fairly complex to build and need precision and would overall be more of a challenge to make one of them than a rail gun. So in light of that I'm using a capacitor bank, it's my most affordable option (cost me 375$ on capacitors and 20$ on silver plated copper bus bars so far)

I think my railgun may be only metal armature. With a plasma armature I need tough materials that are tougher than lexan (what I plan to use) and they may be about the same price but I'm probobly going to have to use standard tools, nothing like milling machines, etc.

I am still designing my rail stack for the gun. so far I've come up a design that uses 2 T shaped spacers that the rails go on wither end of and end up flish with the sides of the T si that it the T's will be covered with a block of lexan and the lexan T's will be bolted to the rail covers. I'm thinking if I use clear polycarbonate I should be able to see all the parts of the gun all the time (untill the lexan gets charred) witch should make for some fairly intersting pictures.

I know already I'll have to keep the rails far enough apart to avoid arcing between them and while minimizing projectile weight. I'm thinking around 10 mm between my rails but I'm not sure yet.

As far as the multiple railgun idea goes, it is possible, beacuse the railgun is just accelerating the slug with an immense current pulse however the energy will be most efficently used if the slug that enters the rails has the entire capacitor bank discharged over one set of rails instead of several.

Most of the velocity's I've seen quoted for railguns are done in the ordinary lab manner in witch they just test it at STP and record the results although I have read of railguns that break the world's speed records by firing into a vacuum. Railguns that fire into vacuum's are VERY fast.

As far as coilguns go I've built a few out of fiberglass tubes and computer grade electrolytic capacitors but they were all single stage and solid state employing hockeypuch SCR's to switch them.

I think a railgun will be much harder than any coilgun and probobly alot more fun too. besides at 4,200V and 7,876 J of energy there isn't much simplicity to design a coil gun of that magnitude

[AfroFukinPyro]

Sam Barros is almost complete his rail gun and in the forum he said full testing should begin as soon as tomorow. Check out this page and go to the rail gun secion (also check out the coil guns).

<a href="http://www.powerlabs.org/" target="_blank">http://www.powerlabs.org/</a>

Edit: That's Sam Barros

<small>[ October 17, 2002, 10:36 PM: Message edited by: PYRO500 ]</small>

[the resourceless reaperman]

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica">As far as the multiple railgun idea goes, it is possible, beacuse the railgun is just accelerating the slug with an immense current pulse however the energy will be most efficently used if the slug that enters the rails has the entire capacitor bank discharged over one set of rails instead of several. </font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">Now what if these sperate railguns each had a seperate capacitor bank? more or less like a coil gun, only instead of coils you use the two bars. It seems like a good idea.

[PYRO500]

That idea would work but it would suck when it came to efficency. the longer the gun the more friction and past a certain point the projectile is destroying any part of the gun it touches (esp rails if you made the gun the right length then you should be able to get the most power out of it when everything is in one stage. Trying to make multiple stages defeats the purpose of building a railgun when you want to get the projectile the fastest speed possible in the shortest distance possible

[the resourceless reaperman]

I see.

Idea:
If the projectile were to be filled with a gas say... Argon. would it turn into a plasma upon firing?

[PYRO500]

What do you mean by filling the projectile with argon? If you mean to make the path of least resistance through a gas instead of directly from metal to metal, yes, some of the gas will get hot and turn to a plasma although that is hardly useful and would be nothing but an arc inside a gas envelope and not do much else. You can use plasma in your railgun to propell a slug though. it involves sending something like a metal ribbon behind the slug and when it's injected and contacts the rails the metal ribbbon should get vaporized and conduct and therefore be subject to the lorenz forces behind the slug and propell the non conducting slug out of the railgun.

[the resourceless reaperman]

does everything that can conductwork?

in case that's so, does salt water ( :p )work?

[PYRO500]

Yes, and no. I think the slug has to be non feromagnetic. Aother thing is that the energy required for that bead of water to go anywere will result in it's vaporization and then nothing will happen.

[the resourceless reaperman]

I assume ferromagnetics mean Cobalt, iron, neodymium etc.

why don't these work? and salt water surely can't be ferromagnetic??

[PYRO500]

Salt water will vaporize! read my last post!

[the resourceless reaperman]

that's not what I asked, I asked why ferromagnetics don't work.

[kingspaz]

the resourceless reaperman, show some respect to moderators. he is trying to help so don't get angry and be grateful. think before you post or face being banned.

[the resourceless reaperman]

Sorry,

I was a bit rude there.

sorry sorry sorry!

I still wonder why ferromagnetics don't work...

[PYRO500]

Because their resistance is too high.

[AfroFukinPyro]

According to Powerlabs, to work properly a railgun must have a pneumatic injector so that the projectile is already traveling around 200 m/s (i think) when it enters the rails.

<small>[ October 20, 2002, 06:07 PM: Message edited by: AfroFukinPyro ]</small>

[Anthony]

It doesn't have to be a pneumatically driven injector. Any means of getting the slug moving before it contacts the rails (at an appropriate speed) will work.

It's interesting to see that Sam Barros' caps are a bit *too* good and he needs to slow the discharge pulse down!

[the resourceless reaperman]

could a strong spring do the job? It won't reach 200m/s but it will be have some speed without the added cost of a pneumatic injector.

[Harry]

How about a double-base injector? Load double-base smokeless into shotshell, add slug, crimp. Prime shotshell, load into chamber. Charge cap bank, ready aim fire.

Harry

[vir sapit qui pauca loquitur]

This idea could be a load of steaming B.S. but.....

from personal experience at a local university and after completing a lot of experiments on the matter i have come to an idea that could revolutionise the entire idea of rail guns and it goes a little like this...

plasma is the fourth state of matter (1-3 being liquid,gas,solid) this is a gas that is highly excited, and as such exhibits strange and unusual properties such as being conductive, plasma can be created by exciting gas (certain gasses) with a UV laser (or by microwave, but a UV laser gives a nice straight line) with 2 uv lasers, one either side of the other generating 2 straight lines straight out (towards target). After the plasma "rails" are generated we then take a light-weight projectile that has fins to aid in stabilisation of said projectile. A potential difference (voltage) is then applied across the two "rails" mimicing a rail gun, the projectile is then 'shunted' in the direction of travel of the rails,
the projectile shorts the two plasma "rails" and it acts exactly as a rail gun would.

Due to the plasma rails, we avoid the usual problems of weight, and damage due to the extreme forces exerted on them. Also this allows for the rails to be extremely long (dependant on the lasers capabilities)

as far as i can see it, this is the way forward (but only if you happen to have a continuos flow of noble gas/uv laser etc :( )

I would love to see if this idea could get off the ground, I may be able to persuade the staff at the uni to investigate this but I would like a bit of feed back on the rail-gun side (not my area) before I start talking about it to anyone else

[PYRO500]

In theroy that idea would work, but there are a few things that stand in the way of success.

One of the things is that you need very huge voltages to conduct electricity down your plasma trails from your multi terrawatt lasers, and another thing is that the air is likely to arc across at the voltage source if you give it enough voltage to arc down two plasma channels.

[the resourceless reaperman]

Why use a railgun if you have multi-terawatt lasers?

[PYRO500]

Exactly the point I was making.

[the resourceless reaperman]

If you have multiple terawatts, wouldn't it be more attractive to use metal bars? why bother about lasers?

<small>[ October 23, 2002, 12:42 PM: Message edited by: the resourceless reaperman ]</small>

[firebreether]

I just saw a picture of Sam Barros' railgun firing, holy cow, that was amazing. quite powerful. Yeah, its too bad that it discharged too fast, you wouldn't think of that as being bad normally :rolleyes: The pulse was so short, that the projectile was only half on the rail and the discharge was over, meaning that it really didn't accelerate the projectile much, just the plasma form the projectile vaporizing. This also made it spectacular to see, as there was a huge cloud of metal sparks, and an intense muzzle flash.

<small>[ October 22, 2002, 11:13 PM: Message edited by: firebreether ]</small>

[Boob Raider]

I am not sure if this would count as a plasma armature (I think it would). Here is the set up. 2 cheap Al railsbolted on a steel plate or something with a couple of mm gap between them. Your cap bank is hook up to the rails like in a regular setup. Now for the projectile ..... a shaped charge with a leaded Cu cone (Cu cone which is allowed to soak in molten lead) or whatever material you think or know is best. From what I know about shaped charges is that they produce a thin jet of metal plasma. The shaped charge is alligned with the rails and detonated. As is the jet of plasma has a velocity of ~10km/s add to which the energy dumped by the caps into the plasma when it moves through the rails.

[Mr Cool]

It may work, but if you've got a SC, then why bother with a railgun? It's not going to accelerate it to significantly more than the ~10 km/s that the tip of the jet is already travelling at without HUGE capacitor banks, and HUGE expense.
Plus, the mechanics/engineering of it would be a nightmare I think, if it is intended to be re-usable. Any misalignment and your jet will just plough straight through your rails and ruin them.

One thing I have been thinkng about would be to have thick copper rails, coated with a mil or so of tungsten, or other non-amalgamating metal. The slug would be teflon or other plastic, perhaps with a metal core. It would be accelerated using a mercury or indium/gallium alloy, or other quite inert liquid metal, as the armature. This would get round problems associated with sparking and welding, and would provide minimal friction. The liquid metal may well vapourise and form a plasma armature I think. If nothing else it would vapourise and propel the projectile via the conventional expanding-gas method, although if that's all that happens it'd be a bit of a waste of time!

[Boob Raider]

Why not use a slug of Hg or Hg/Ag amalgam instead. I believe the teflon wouldn't allow the slug to accelerate to a large extent as it is non-conductive. I believe only the Hg/In plasma would accelerate. Personally Ag slugs should be the simplest and best. Least electrical resistance of all metals so no arcing or welding problems. I am not sure is welding a greater problem or friction with the rails. If friction is a greater problem the Graphite looks pretty good. Like I said earlier Hg/Ag amalgam would be good too.
I didn't know that the caps wouldn't be able to accelerate a plasma jet over ~10km/s.
The reason I thought so is that in every railgun related page that I have read, it is mentioned that the faster the slug is traveling before it enters the rails the better. And I believe the military railgun has the slug explosively projected through the rails.
I wasn't worried about the rails getting damaged part. I was using cheap Al rails to begin with.

[Mr Cool]

"Why not use a slug of Hg or Hg/Ag amalgam instead. I believe the teflon wouldn't allow the slug to accelerate to a large extent as it is non-conductive. I believe only the Hg/In plasma would accelerate. Personally Ag slugs should be the simplest and best. Least electrical resistance of all metals so no arcing or welding problems. I am not sure is welding a greater problem or friction with the rails. If friction is a greater problem the Graphite looks pretty good. Like I said earlier Hg/Ag amalgam would be good too.
I didn't know that the caps wouldn't be able to accelerate a plasma jet over ~10km/s.
The reason I thought so is that in every railgun related page that I have read, it is mentioned that the faster the slug is traveling before it enters the rails the better. And I believe the military railgun has the slug explosively projected through the rails.
I wasn't worried about the rails getting damaged part. I was using cheap Al rails to begin with."


Arcing, welding and errosion are serious problems with all solid armatures. With a liquid armature, there could be no welding, and minimal sparking due to the intimate contact between the armature and the rails. To get such an intimate contact with a solid armature would add a great deal of friction in comparison.
That is the reason for using a liquid armature.
A liquid slug, as the projectile, would be no good since it would easily vapourise due to the currents, meaning that you no longer have a projectile, and if it did survive there's no way that a drop of liquid would be stable flying through air at several km/s.
The teflon slug would not need to be conductive since it is being propelled by the armature. It would be accelerated just fine due to the huge force exerted on it by the accelerating mercury armature. There is no way that the armature could accelerate without accelerating the teflon slug.
"Least electrical resistance of all metals so no arcing or welding problems."
The contact between armature and rails will have a significant resistance, leading to arcing and welding.
"Graphite looks pretty good"
In my experience, graphite shatters way too easily. When it contacts the rails, resistance (which is quite high, even without contact problems) causes massive heating, also there is arcing, and the resultant stresses blow the graphite into little chunks. Although that was with artist's graphite sticks.
"I didn't know that the caps wouldn't be able to accelerate a plasma jet over ~10km/s."
They could do it, but even with a VERY VERY VERY good and expensive design you're very unlikely to get more than a few km/s extra. Meaning that you would have spent many $1000's to get from 10 km/s to 12 km/s, when the first ten only cost you $5 for a SC. Just think what sort of damage you could do with an equal amount of money spent on SC's!!!!!
"it is mentioned that the faster the slug is traveling before it enters the rails the better."
That is very true, I see what you were thinking. I just don't think it'd be at all practical!
"And I believe the military railgun has the slug explosively projected through the rails."
Explosively, perhaps. But not SC jets. Also, they have multi-MJ cap banks, which could provide significant acceleration compared to the injection speed.


Edit: I just read through my reply, and it sounds a bit rude. It isn't meant to :).

[silverleaf]

One thing though, if you use high enough energy to get high speeds, then there is the chance of the rails flexing, due to the magnetic field's effect on the metal in the rails, plus too much energy and the projectile may weld to the rails, due to arcage, like that in an arc welder, but one way to curve this, is based on the principal, that the field strengthens with distance, so that a low force over a longer rail-set, will yield super-high speed, without any arc risks

[zhuge liang]

Could the spacing between the rails be far enough so that when the armature is shot between the rails the arc could accelerate the projectile? And it may eliminate the question of capacitors. Also, the pre-accelerator could be a crossbow, yes?

Also, if you used a thin needle of a solid material, then would it not fly faster, as well as vaporise, when fired?

(In future don't post twice, us the edit function so i don't have to glue your posts together - kingspaz)

[Jacks Complete]

There is a trick you can use to double the effective power out of your railgun, which is very handy when you are dumping your power too quickly. The answer is to bend your rails, as per the patent I read once (Darned if I can find it though). Basically, the design calls for double length rails, which are bent back round, to run along with the opposite rail. The current is injected in the usual way, but because of the "extra" turn in the rails, the inductance goes up a bit, meaning that the current is driven through slower. However, this is offset by the greater force acting on the armature. This also reduces problems such as arc-over and flash vapouring your projectile!

The one I tried to build ended up being a very good spot welder. Heated the projectile and spot welded it to the rail when the "injection" was done by rolling a steel ball bearing down a cardboard tube and onto the rails. Faster injection just meant all the way down the rails was covered in little spot welds!

[s9ar7acu3]

Google:Ram Accelerator

http://www.google.com/search?hl=en&lr=&ie=UTF-8&c2coff=1&q=Ram+Accelerator&btnG=Search

Ram> Rail gun

Positively Scalable (efficiency goes up the bigger it is)
Simple(er) to fabricate
Chemical reaction as opposed to Complex electrical system, hence cheaper.

[FUTI]

This Ram accelerator is very interesting and I wonder why I didn't heard about this before.

Do you think that sprayed diesel can be used for RAM accelerator just for testing purpose of course?

It should ignite on compresion and you could use an air cylinder to accelerate the projectile to compress the mixture to ignition point. Do you think this can work?

I think that 7 to 11 km/s is the highest velocity measured with rail or coil guns. It was interesting subject around WWII and now and then someone try something in this direction but no big breaktrough so far. My advice...abandon the project. I would rather play with chemical lasers (which are also suspiciously effective) then railgun.