# Talk:Railgun

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## Math inconsistency

I corrected the math in the "mathematical formula" about 3 years ago. Yet someone reversed the correction. One should not calculate the Lorentz-force due to a complete current-carrying wire but only half such a wire, since at the location of the bullet, the current goes through the bullet (and not further along the same rail) and then back along the other rail. So the magnetic field in between the rails is just the half of what's written now (at least, before I correct it again)! 193.190.253.144 (talk) 13:50, 10 May 2013 (UTC) I have just corrected the text to correctly explain your corrections, i.e, to clarify (I) the equations give the armature field from semi-infinite wires and (II) because the wires are semi-infinte, the field expression is only valid at the armature and not as any axial position between the wrires as the previous text suggested. — Preceding unsigned comment added by 82.132.239.173 (talk) 12:17, 23 August 2013 (UTC)

## Navy-centric?

Here are some hints about a comparable army program that seems much more advanced: Railgun Pulsed Power Program 76.126.215.43 (talk) 19:34, 12 July 2009 (UTC)

## Removed the image

Railgun? I think not. The image appears to be taken from this video http://www.dvidshub.net./?script=video/video_show.php&id=34650 The first bit of the video appears to be the same facility the U.S. Navy was using in 2006 for RG test & dev. However, watching the video closely at a slower frame-rate shows the projectile is propelled by an internal propellant. Chances are the photo/video is mis-labeled. Compare this video (projectile design, lack of combustion during flight, etc) to the 2006 testing, seen here: http://www.youtube.com/watch?v=y54aLcC3G74

Then the conspiracy theories starting kicking in and I wonder "Would Navy testers use a rigged flame producing projectile to make it appear to not be a Railgun?" —Preceding unsigned comment added by 123.112.10.105 (talk) 14:52, 6 April 2008 (UTC)

No, that image is correct. The flame you're seeing behind the projectile is actually plasma. The plasma is created when electrical arcing occurs inside the barrel of the gun (when the aperture breaks contact with the rails). That and the generally high temperatures within the barrel causes the air to become superheated and eventually plasma. The blue flame also appears to be some kind of plasma effect, though it's more likely just from air friction (the projectile is traveling around 2500 m/s, Mach 7)). See: http://www.youtube.com/watch?v=i1q_rRicAwI The first second or two shows the (what I assume to be) the official navy label of the video. It was their latest 'record setting' test fire of the railgun that will eventually be mounted on one of their new boats. —Preceding unsigned comment added by 18.244.3.105 (talk) 01:52, 14 December 2008 (UTC)

## Current Events

Apparently the US navy HAS developed a real fully functional rail gun and plans to put them in use by the year 2020. For more info check out this article at http://fredericksburg.com/News/FLS/2007/012007/01172007/251373 So if someone can please update the article? Lab Dragon 22:08, 17 January 2007 (UTC)
It is BEING developed. If it was developed it would be a year or two away, tops. 2020 is what there aiming to have an operational one for. Current models are experimental. 69.115.70.122 (talk) 00:09, 8 November 2011 (UTC)

## More Recent Events

There isn't much about how the progress on railguns in the US Navy is doing in this article, but it seems that power may no longer be a problem:
According to sources, the AoA looked at two possible nuclear powerplants based on existing designs: doubling the single-reactor Seawolf SSN 21 submarine plant, and halving two-reactor nuclear carrier plants.
Doubling the 34 megawatts of the Seawolf plant would leave the new ship far short of power requirements — and not even match the 78 megawatts of the Zumwalts.
But halving the 209-megawatt plant of current nuclear carriers would yield a bit more than 100 megawatts, enough juice for power-hungry BMD radars plus an extra measure for the Navy’s desired future directed-energy weapons and railguns.

http://www.navytimes.com/news/2007/07/defense_cgx_070723/

Also, railguns have been used to initiate fusion reactions, by firing pellets of fusible material at each other. The impact creates immense temperatures and pressures, allowing nuclear fusion to occur.

That's really interesting. Can you provide a cite?

Look at http://www.physics.northwestern.edu/classes/2001Fall/Phyx135-2/19/railgun.htm, I think that it theoretically could be used to create fusion rather than has been. I will wait until the author has a chance to provide a cite before changing the article. -- Chris Q 09:57 Apr 30, 2003 (UTC)

Hmmm, I can't remember where I first heard of the idea, but this page has a mention:

http://www.physics.northwestern.edu/classes/2001Fall/Phyx135-2/19/railgun.htm

Looks like I might have been mistaken about it having been done! I'll go through my list of railgun bookmarks to see if I can find the original reference, but will change it for the time being.

Google has come up with many links about using railguns to inject fuel pellets into certain kinds of fusion reactor, too.

Most of these articles relate to using a railgun to inject the hydrogen fuel pellet into a magnetically confined plasma (ie tokomak), not actually smashing pellets together. —Preceding unsigned comment added by 68.187.71.106 (talk) 20:22, 19 March 2009 (UTC)

(beware science fiction sites!)

Lots of good links that I need to add to the page, I think...

Alaric 10:07 Apr 30, 2003 (UTC)

Hmm, given the sudden spate of edits on this new article, I'd think there had been an enormous amount of untapped interest in railguns amongst the Wikipedian crowd, for some reason. ;-) -- John Owens

Indeed! Sorry I mangled your comment, resolving the conflicts on each update was getting confusing -- Alaric 10:50 Apr 30, 2003 (UTC)

In The Moon Is A Harsh Mistress, they do not use a rail gun.
The projectiles used there are ferric vessels filled with rocks; the accelerator uses magnetism to push & pull, not the railgun effect.
--Einstein9073 21:43, 2004 Nov 19 (UTC)

There are a couple of points that I don't understand, which could possibly be :explained in the article.
Firstly, won't there be a force equal to that on the projectile pushing the :rails apart? Given the high level of force, how can they withstand this?

By being made of tough stuff (they are likely to be thick metal anyway to withstand the current without overheating) and by trying to optimise the design to ensure that the magnetic field is bunched around the projectile rather than the rails. There is also a recoil felt on the rails, but that's along the rails, the direction in which they're strongest. I will clarify the section about the physical stresses on the rails. -- Alaric 10:50 Apr 30, 2003 (UTC)

Actually, the force separating the rails is one of the greatest issues with using railguns. A tough, heat-resistent, superconductive material simply has not been found, and rails have been known to split apart in tests. Take a look at the How Stuff Works article. It's in the science section under Engineering. I also have several other sources for this, but I don't have time to cite them. CommKing 01:14, 25 March 2006 (UTC)

Secondly the article says:
Railguns only fire bullets, not shells?. Shells depend on their arrival at the target being more violent than their launching, so they can be detonated by impact without detonating in the barrel of the gun. However, being fired from an anti-tank railgun is more violent than hitting a tank (the projectile accelerates to maximum velocity in the space of a metre or two, but when it hits the tank it punches straight through and decelerates for several metres)...,
Surely a conventional shell only accelerates (at most) through the length of the gun barrel. Whereas the acceleration needed to reach 150km/s would be too much for a shell, you could reduce the current to give an equivalent acceleration of an explosively-propelled shell. Wouldn't it be more accurate to say that the advantage of a rail-gun is that it does not require an explosive shell, rather than saying that it cannot use one? -- Chris Q 10:37 Apr 30, 2003 (UTC)

You could indeed build a small railgun that is used to launch shells, yes, but I've not heard of any interest in doing so. I'll mention that. -- Alaric 10:50 Apr 30, 2003 (UTC)

The heating effect of the current in a railgun means that the projectile often leaves the barrel molten - this is clearly unsuitable for a shell.

I remember reading from somewhere that the use of railguns as artillery has been considered since World War I: the lower noise and lack of muzzle flash or smoke when firing the gun would have been a big advantage back then. -- Erzengel 11:16 Apr 30, 2003 (UTC)

I believe you might have that confusion will the original definition for railgun. It probably should be mentioned in this article that the weapons first known as railguns, short for railroad guns, are howitzers mounted on train cars, like the Paris Gun or Big Bertha. EisenKnoechel

Just to avoid any weapons country getting a patent I think I should point out that plasma windows described in http://flux.aps.org/meetings/YR97/BAPSDPP97/abs/S5800006.html and other places have obvious uses in railguns. The gun could be in a vacuum, firing through a plasma window, eliminating air friction until the projectile is released. This would reduce the damage to rails from fragments of the projectile, oxidation etc. -- Chris Q 09:48 May 1, 2003 (UTC)

## Railguns in the navy

Railguns were also experimented by the U.S. Navy, but have proved impractical with the current designs. Just for all those people who don't know. -Someone named Volos.

There's a paragraph about naval railguns in the "Railguns as weapons" section, feel free to expand on it if you know any details about how research in that area's been going. :) Bryan 20:36, 5 Jun 2004 (UTC)

I've heard that the rail gun tech could also be used to lauch fighters off the deck of an aircraft carrier. DoSho 13:34, 25 Jun 2006 (UTC)

It could not be used with current fighter technology as the wings of the aircraft would disintegrate as soon as it was launched. The use of railguns to launch fighter aircraft will have to wait until wings are no longer required for flight. -From your friendly neighbourhood Aussie

A railgun could launch a fighter if the railgun accelerated a carriage that launced the aircraft. However, linear induction motors are used to do this instead. —Preceding unsigned comment added by 216.229.75.63 (talk) 03:38, 10 November 2007 (UTC)

Friendly Neighborhood Aussie - Right, and because the US Navy uses steam in its current catapults, they must shove the plane in a steam pipe. Nothing says the railgun has to accelerate the plane to kilometers per second, especially if its providing motive power to a 20,000 kg load instead of the 3.2 kg the USN is using. —Preceding unsigned comment added by 86.219.6.30 (talk) 22:19, 2 February 2008 (UTC)

I think its a bit misleading and ultimately useless to compare the projectile velocity of a rail gun to that of a M16. It is apples and oranges. The rail guns in development are massive and power hungry, meant to be mounted on warships, whereas the M16 is a man-portable assault rifle. I think a ship mounted cannon or a howitzer's muzzle velocity would make better comparisons. I suppose it could be argued that the M16 muzzle velocity is stated to have it be a more accessible figure, but not many people have actually fired and seen the rifle in action themselves. 76.111.88.167 (talk) 02:30, 26 September 2008 (UTC)

An electromagnetic launch system is being built as well as a carrier to go with it. see: http://defensetech.org/2014/05/13/navy-to-test-electromagnetic-catapult-on-carrier/

Arydberg (talk) 11:36, 15 September 2014 (UTC)

## Too vague. it is postulated?

The artical says: It is postulated that the next generation of reactive armour will be impenetrable by conventional ammunition and shaped charges.

I think this is a bit vague By whom? Is this a reasonable postulation? within what limits - presumbreach the aemour.

Reactive armour only works onece It is just pieces of explosive that explode and hit the incomming projectile rective armour has nothing to do with penitration except to repell incoming shells DudtzFile:Kardos.jpg 7/21/05 1:43 EST

## Railgun in Stargate Atlantis!

WOW, it is wonderful! I like it so much. Hope to see it more in the second season blasting the Wraith's heads!

## Glitter Boy

A lot of us RPG players were introduced to Rail Guns by the Glitter Boy http://en.wikipedia.org/wiki/Glitter_Boy

## Railguns in Video Games

I think this warrants its own heading in the article, because sci-fi doesn't really fit for me - it implies either written fiction or TV/film. Thoughts? Tiefighter 08:36, 16 Jun 2005 (UTC)

I think it doesn't. I periodically trim the list down to the most significant few, because otherwise, it would grow to the point where it takes over the article, as everyone adds their favorite reference. Weapons called "railguns" appear in a great many science fiction and video game settings. --Carnildo 17:50, 16 Jun 2005 (UTC)
The heading is fine as is is I think. How ever the entries put there need some controling. The current EVE Online paragraph isn't really required as it is. Any mention of games/film/books etc should stick to describeing the portrayal of the technology, and not go into unwanted detail of game mechanics and the likes of 'the railgun can be upgraded with the blue unit for 5 more damage'. etc... 194.75.238.138 13:47, 9 May 2007 (UTC)

## Competing/alternative technologies?

Maybe it would be useful to link this page to http://en.wikipedia.org/wiki/Project_HARP (Gerard Bull's Supergun) and possibly other pages related to launching projectiles?

People can find those by looking in the article's category. ··gracefool | 13:19, 19 September 2005 (UTC)

## Another game with Railguns

Fallout 2 and Fallout Tactics: Brotherhood of Steel are two post-nuclear-apocalypse RPG PC games that make use of such weapons.

As does Timesplitters 2 & 3 —Preceding unsigned comment added by 96.226.243.32 (talk) 15:45, 30 August 2009 (UTC)

## Recoil Issue

I read somewhere that railguns would not have a serious recoil issue due to the fact that the projectile is in effect being carried out of the barrel by the magnetic forces.

Conservation of momentum will still apply, so whatever force has been applied to the projectile will also be applied to the barrel in the opposite direction. --Martyman-(talk) 23:39, 12 November 2005 (UTC)
Sweet, thanks for clarifying that. It's always fun to learn off Wikipedia. Karmon 00:58, 1 December 2005 (UTC)

Actually, while the physics are the same (obviously), the recoil for a given projectile in a rail gun is less than for a conventional gun. All other things being equal,the accelerated mass is less in a rail gun because there is no propellant. In addition, there are more structural options for dealing with reaction forces in an electromagnetic system.

Googling the exact subject -"Railgun Recoil"- shows there's actually a lot of controversy regarding this. A number of experiments show railguns producing less recoil than one would expect. It seems to be a loophole in the conservation of momentum!Kalaong (talk) 01:26, 6 May 2008 (UTC)

You have any published studies supporting this? Didn't think so.- (User) WolfKeeper (Talk) 01:45, 6 May 2008 (UTC)
I will now snipe you from six miles away and watch your body make a crater in the wall. [1] You've just been erased!-Kalaong (talk) 18:52, 6 May 2008 (UTC)
There is recoil, however it is directed in a different direction due to the nature of the magnetic fields. Most of the recoil is directed sideways, threatening to bend the rails laterally, instead of backwards as traditional firearms direct recoil. Thus, this sideways recoil is not noticed by the shooter... unless the rails of the gun are not securely mounted. 24.131.148.131 (talk) 20:44, 3 June 2009 (UTC)LeftHandSum
Don't be ridiculous. There is recoil, and it is opposite in direction to the motion of the armature. Anything else violates Newtonian mechanics (actually Relativity theory.) Relativity theory is intimately related and can be derived from E-M theory and relativity has been validated (quite literally) billions of times in particle accelerator as well as various astronomical observations.- (User) Wolfkeeper (Talk) 22:13, 3 June 2009 (UTC)
There's nothing magical going on here, if you take a coil of wire and put current through it the coil tries to expand- and this is true whatever shape the coil is. A railgun is just an oddly shaped coil.- (User) Wolfkeeper (Talk) 22:13, 3 June 2009 (UTC)

Wouldn't the 'seat of the recoil force' be the magnets that are on and affecting the bullet, with the direction of force being towards whereever the bullet is? (Eg. The magnets are pulling themselves towards the bullet; but since they can't move, the bullet comes towards them; but that doesn't mean they aren't still trying to move towards the bullet.) 75.164.163.75 (talk) 17:02, 8 June 2009 (UTC)

Don't be rude wolfy, It's all about kinetic energy and momentum. Since railguns can fire projectiles @ higher velocities, the momentum (aka recoil) is less than a conventional gun for a given muzzle kinetic energy (aka DAMAGE!), but the effects are gonna be nasty: with disintegration of the projectile on impact and making shockwaves in WATER @ 6Km/s, you can blow up someone while barely noticing you have just fired it; assuming you fire in vacuum, since the air itself disintegrates the projectile @ such a velocity. —Preceding unsigned comment added by 91.99.165.66 (talk) 11:07, 10 May 2010 (UTC)

## Railguns in science fiction

I have moved the scifi section to it's own article, and replaced it with a short summary. I think one of wikipedia's largest faults is the prevalence of pop-culture references drowning otherwise valid articles. Please discuss here if anyone has a problem with this. --Martyman-(talk) 22:55, 15 November 2005 (UTC)

## Peaceful Use

I would assume a "railgun" placed in a coil would act much like a particle accelerator. Is there a point that a projectile would no longer "touch" the rails and be a self-sustaining moving object - presumably in a zero-g environment? On earth, perhaps putting the "coil" on an axis and forcing a tilt to use gravity as an accelerator? Basically, is there a point (much like a magnetic "engine") that the object would cease movment if placed on a designated track inside a continuous loop rail gun? (think "O") - Amejin

I don't quite get what you mean, but if the projectile stopped touching the rails then it would stop. --SHCGRA Max 12:52, 2 September 2006 (UTC)

## History

If anyone is interested in adding the history of railguns into the article this paper seems to have a decent history of railguns up to the end of WW2: http://ieeexplore.ieee.org/iel4/20/15929/00738413.pdf?arnumber=738413 128.12.90.56 15:41, 20 April 2006 (UTC)

That's certainly a good recomendation and the author (Ian McNab) provides a very comprehensive list of references and acknowledgements for all his sources.

I removed "

German railgun diagrams

" because it's a forgery. A rectangle is used to denote a resistor in Germany, while a zigzag line is used in the US: http://en.wikipedia.org/wiki/Resistor#Electronic_Symbols_and_Notations — Preceding unsigned comment added by Deathmare (talkcontribs) 18:19, 1 March 2012 (UTC)

## Pictures/Bullet at high speed?

At the top of the page it says the article needs more pictures theres a good one at http://images.military.com/pics/SoldierTech_Rail1.jpg i dunno whether you can use it or not thats a copyright issue. completely different topic now wouldn't a projectile fired at such high speeds as mentioned in that article melt a bullet or at least deform it? Probably wouldn't effect the penetrating abilities of a bullet to much at that speed but maybe somewhere could be gone with that... Also I think this should bump the other picture under rail guns in video games but of course im biased on that one... its just cooler http://upload.wikimedia.org/wikipedia/en/4/48/Metal_Gear_Solid_-_Metal_Gear_REX.jpg MetalGear2698 07:47, 29 November 2006 (UTC)MetalGear2698MetalGear2698 07:47, 29 November 2006 (UTC)

## Glaring error - conservation of momentum

"Additionally, the recoil of a hand-held weapon is not solely dependent on the momentum of the projectile."

Yes, the recoil isn't solely dependent of the momentum of the projectile, but it's completely dependent on what comes out of the barrel. I'm studying physics, and this is a pretty clear error--the article implies that traditional guns violate the conservation of momentum principle, which isn't possible. I don't know much about guns, but I'd guess the extra recoil from gas-propelled would come from hot gas rushing out of the front of the barrel. A railgun wouldn't have this problem.

-Danny

If you read the rest of that section, it becomes clearer. If two guns have the same total recoil (ie, deliver the same impulse when fired - measured in units of momentum, such as sN), but one delivers that impulse over a longer period of time than the other, then the practical effects of the recoil will be different. The word 'recoil' is being used to refer not just to the magnitude of the impulse, but to the graph of impulse vs time over however long the gun takes to fire - which seems consistent with definitions of the word that I've seen.
If it misled you, though, that suggests that it may need to be rewritten to be clearer. I'll take a look when I have some more time. --144.136.185.68 13:50, 22 May 2006 (UTC)

Im in first year engineering, and in our standards physics problems to do with "force exherted by firing a projectile of this mass at this velocity" force exherted could be intermitedly changed with force of recoil. What im trying to say is that i agree with danny on how the article should be written, because when i first read that I also disagreed. And the following explanation is somewhat vague. Maybe only keep the part of how shock absorbers could reduce the effect of the recoil. I'm not going to change that part of the article as if i did anything it would only become more vague. -nick

It sounds to me like the way you're using the word recoil - ie, to mean 'force exerted by firing this projectile' - is perfectly consistent with the use of the word in the article. After all, this force is not solely dependent on the momentum of the projectile - it's related to it by the equation p = F*t, where p is the momentum of the projectile, F is the force on the projectile (equal in magnitude to the force on the gun, assuming no exhaust gases), and t is the time over which the force is applied. (Strictly speaking I should be integrating F with respect to t, but this approximation is close enough if F is constant.)
I strongly disagree that the paragraph should be cut down to a mention of shock absorbers. There's a real effect that it's describing - it just needs to be a little bit clearer. I've rewritten the first couple of sentences, to try to accomplish this. Has it worked? --144.136.185.68 09:00, 23 May 2006 (UTC)
I'm the guy that originally wrote in the recoil bit. Personally, I find it less comprehensible now. Let me try again. Basically, I was trying to say that perceived recoil is extremely different from the "actual" recoil impulse. Recoil impulse determines what the final velocity of the gun is--no more, no less. Recoil force, on the other hand, determines what the recoil feels like. It's like the difference between suddenly braking from 55 mph to 0, and crashing into a tree at 55 mph. The impulse is the same, since you go from 55 to 0 in both cases, but the force... Arrkhal 05:36, 24 May 2006 (UTC)
Yes, that's the effect. Although impulse is significant too - to extend your analogy, compare the effects of crashing into a tree at 55 mph with a crash at 5 mph. (You can have a ridiculously high force but, so long as the impulse is insignificant, the recoil will not be noticeable.) I'm having trouble, however, thinking up a simple way of explaining it. --144.136.185.68 11:35, 24 May 2006 (UTC)
Well, I usually prefer to use velocity and acceleration to describe recoil, rather than momentum and force. Final velocity and acceleration are really what you feel. For instance, .357 magnum in a snubnose revolver is very unpleasant, but the same load out of a full sized rifle, despite the higher velocity (and thus momentum) is extremely mild. Basically just that acceleration (and thus force) isn't much of a factor if the final velocity is low, but can be a real problem if the final velocity is high. Arrkhal 05:20, 25 May 2006 (UTC)
The simple way to explain recoil is, "every action has an equal and opposite reaction". Jason S. 02:28, 14 June 2006 (UTC)

Close to half the recoil impulse in conventional guns is from the gas being shot foreward, which is why you see muzzle breaks and rarefaction wave guns and in the other direction, recoiless guns.

energy will tell you the distance it takes to stop something, for a given force. momentum will tell you the time it takes to stop it with a given force.

"recoil impulse" and "felt recoil" is the distinction you're looking for. felt recoil is different from the physical recoil impulse because people would much rather feel a 50lb force for one second than a 5000lb force for .01 seconds, anything that spreads out the recoil force, and keeps the firce in line with the 'piston' absorbing it is a good thing. check out the HIWS, and the KRISS for examples.

the reason you feel less recoil with the rifle than the pistol, despite the higher velocity, is that the rifle absorbs less energy from the shot than the pistol will, despite gaining more momentum. Solve the M1xV1+M2xV2=0 for momentum with the M1xV1^2+M2xV2^2=2xEk for energy and you'll see. This is the same reason for example that this 20mm rifle has a 35lb weight screwed onto to the barrel. This is also the reason they tell you to keep your rifle tight into your sholder, this way the system acts more like your sholder is part of the weapon. The forces make it to your sholder during firing, insted of bullet to weapon then weapon to sholder, effectivly making the weapon heavier, reducing energy transfer.

## Projectiles

I am attempting to construct a railgun for a school related science expo. While I understand the basic concept behind it, there are many questions I have yet to figure out answers to. After reading Wikipedia's page on railgun physics, I have most of my questions answered, however there is one more that i can't figure out: what different kinds of materials can be used as projectiles? The page simply refers to the projectiles as "electrically conductive projectiles". Would this include such things as water or aluminum? while both of these things are in fact conductive, i don't see how any type of magnetic field could have any effect on them. Is the page really accurate by leaving this field open to just ANY electrically conductive material?

Bradley Gefroh209.112.152.222 06:37, 5 April 2007 (UTC) (biggie360@hotmail.com)

Yup, (salt) water and aluminum would both, in principle, work as railgun projectiles. The salt water might not work so well as the aluminum, mainly because it's hard to maintain the integrity of a blob of water. The aluminum, at least, is solid and therefore won't simply splatter all over the barrel. Railguns don't need ferromagnetic materials (as do, say, coil guns) -- you're using the Lorenz force to push the projectile, and that only depends on the strength of the magnetic field and the amount of electric current passing through the projectile.

The physical limit on railgun projectile speed is set by the resistance of the projectile, and by how much heat it can absorb. Making it go faster requires more electric current, which heats it more. Eventually the projectile vaporizes before it leaves the gun. zowie 18:52, 5 April 2007 (UTC)

To my knowledge most currently produced railguns use an aluminium projectile in a sabot casing. I think it is safe to say that any electrically conductive low heat conductive material would work. It would be interesting to see if titainum is a plausible metal to use. —Preceding unsigned comment added by 69.136.222.225 (talk) 02:22, 23 April 2008 (UTC)

Don't waste your time, a coilgun is better anyway. (hope it's not too late to say that!)

## Expressing the Force vector as a function of I and d

I was wondering if someone may be able to quantify the magnitude of the force vector produced and how it corresponds to the current and distance between the rails, and include it in the article. 169.139.221.252 20:37, 11 April 2007 (UTC)

-- I think I've figured it out, though I'm not a mathematician, so I won't edit the article to add it in; someone more experienced in the subject field may feel free to correct me or make the necessary changes. I derived this from the magnetic field density and lorenz force equations, where d is the distance between the centers of the rails, r is the radius of the rails, I is the current, and F is the lorenz force in Newtons.
P.S. I don't know LaTeX. Have a .png: http://i14.tinypic.com/2nixxr8.png Cunjo 23:24, 12 April 2007 (UTC)
-- let's see if this works...

$F = \frac{\mu_0 I^2}{2 \pi} \ln{\left | \frac{(d-r)^2}{r^2} \right |}$

-- The formula that are found in this document say:

$F = \frac{\mu_0 I^2}{2 \pi} \ln{\left | \frac{r+d}{r} \right |}$ Can someone verify which one is correct ? —Preceding unsigned comment added by 81.245.62.162 (talk) 19:44, 21 January 2008 (UTC)

-- I calculated the formula in the article. If you have a source for that, it would help me to evaluate it. I am not finding said formula in the document you linked. It is possible however that the variables d and r between the two formulas refer to different factors. In mine they were arbitrary variables for the distance between the rails and the radius of a single rail. 131.247.244.188 (talk) 21:47, 28 February 2008 (UTC)
-- I have also calculated the formula in this document, and in my mind it seems to be reasonably accurate (considering the assumptions made). The formula is in page 8 of the document((formula (20)). I am a mathematics and physics student, and when I discussed about my calculations with my teatcher at the university, he said that the calculations seem okay. So im going to edit the formula in the article. And by the way, the situation is just as the previous writer (131.247.244.188) said; the variables d and r between the two formulas refer to different factors. In the formula $F = \frac{\mu_0 I^2}{2 \pi} \ln{ \frac{r+d}{r} }$ the $d$ is the distance between the closest points of the two circular rails, and $r$ is the radius of the rails, whereas in formula $F = \frac{\mu_0 I^2}{ 2\pi} \ln{ \frac{d'-r}{r}}$ the $d'$ is the distance between the centerpoints of the rails and $r$ is the radius of the rails. So, $d'=d+2r$ and $d'-r=d+r$ —Preceding unsigned comment added by 194.29.195.10 (talk) 16:21, 29 February 2008 (UTC)

## Error: Source does not say railgun will replace Tomahawk

I read the article cited as reference number two. It neither says nor implies that the Tomahawk missile will be replaced by a railgun. It simply says the railgun will deliver the "punch of a Tomahawk cruise missile" at "bullet prices" because of the tremendous kinetic energy of the projectile. Railguns cannot currently replace the Tomahawk because of other considerations like accuracy at long range, and terrain intervening in the trajectory, not to mention the problem of loss of kinetic energy downrange due to air resistance. Further, in order to be effective, the projectile must be able to transfer the energy to the target. A non-explosive projectile striking a light target like a wood-frame building will simply punch a hole through it and continue on, taking most of its energy with it. Putting an explosive projectile into a railgun is problematic, because of the need to limit the acceleration to prevent detonation of the column of explosive by the shock of firing. Low acceleration requires a longer barrel, which is problematic given the limited space on a ship and the high projectile energies being described. I'm going to correct the erroneous statement in the article.
Psminson 21:34, 8 May 2007 (UTC)

## "Simplified Explanation"

I think that this section is poor form. It's exactly what it says, but I've never seen another wiki article with a recap-for-junior-high-school at the bottom. I feel that the section should be removed or integrated into the introduction. 69.159.77.70 16:56, 11 May 2007 (UTC)

• I agree and removed it. Saw no information in it that was needed in the rest of the article. And having an article "recap" would set a silly precedent 69.114.83.91 (talk) 08:06, 3 February 2008 (UTC)

## railgun vs. coilgun

The railgun and coilgun articles both protest that they are not the same thing, but neither explains what the differences are. Would someone be willing to rectify this?--Father Goose 01:43, 24 June 2007 (UTC)

I'm just taking a guess: Railguns repel the projectile out of from the cannon rather than using a series of coils that attract the projectile one after another towards the opening of the cannon. Anyone think that sounds correct? --Trakon 09:41, 24 June 2007 (UTC)
Well, it looks like the difference is that railguns use a charged projectile which is propelled via the Lorentz force, whereas a coilgun relies on the more familiar principle of ferromagnetism. But I'd like to see a layman's explanation of how those two phenomena are different, and I'm not the person to write that explanation.--Father Goose 23:44, 24 June 2007 (UTC)

Railguns use electromagentic force(pressure) to generate acceleration by pushing the projectile, ie replacing the conventional gunpowder generated force. A Coilgun uses stages of electromagetic fields to pull (slingshot) the projectile forward and creates less pressure force but runs into diminished power and projectile size issues. —Preceding unsigned comment added by 69.136.222.225 (talk) 02:29, 23 April 2008 (UTC)

The simplest difference is that the projectile is part of the circuit on railguns and it is not on coilguns. Said another way: Railguns run current through the payload and coilguns do not. —Preceding unsigned comment added by 165.91.10.87 (talk) 06:26, 24 October 2009 (UTC)

Coilguns use one or more coils to ATTRACT (or repel, though not much efficient) a FERROMAGNETIC projectile (preferably steel and iron) to an UNLIMITED (not more than speed of light!) speed. Their problem is the SWITCHES that don't explode into plasma when turned on. Railguns use two parallel rails to accelerate a CONDUCTIVE projectile to a speed the plasma formed by ABRASION between rails and projectile allows, by a current running through the rails, projectile, and plasma layers. Their problem is the previously mentioned abrasion that eats RAILS away gradually and terrible EFFICIENCY. The winner is coilgun for simple construction, minimum abrasion, higher efficiency, and no speed limit. The current is applied by charge stored in capacitors, the main problem that prevents these weapopns to be common and useful, due to limited energy and power density. —Preceding unsigned comment added by 91.99.164.42 (talk) 19:14, 27 January 2010 (UTC)

## CARMAC?

Are there any sources that the acronym "CARMAC" is really used? It has a stunning resemblance to the last name of John Carmack, a video game programmer who created the games of the Quake series, where the railgun is a very popular weapon. (91.64.123.40 12:26, 3 August 2007 (UTC))

Good catch. I can't find a single reference to either CARMAC or CARMAG that isn't derived from this article. I removed them.--Father Goose 18:34, 3 August 2007 (UTC)

## Supergun/BigBabylon?

The artical speculates that Saddam was developing "the supergun" as a rail gun. I believe this is an fallacious association. I've never seen a reference to the supergun that didn't describe it as a (usually multistage) explosive charge based design. G.Bull, it's designer, also lacks association with railguns. The article specifically on the Supergun does not refer to it as a railgun and the pictures of it in that article look to be of a fairly conventional design. Lastly the attributed source does not state that the supergun was a railgun, it states that Saddam had unsuccessfully invested in various weapons' research in addition to the Babylon Project;

"There was a reported program to create a "rail gun," in which electromagnetic pulses would accelerate a projectile to high speeds, research on elaborate multistage rockets and re-entry vehicles, and, before 1991, endless tinkering with weird biological agents. None of it produced anything particularly useful." —Preceding unsigned comment added by 67.32.149.42 (talk) 21:37, 31 October 2007 (UTC)

## What the hell is the difference?

Both articles: coilgun and Railgun specify in their introductions that they are not to be confused by each other.

And that is the only mention they have for each other.

What the hell is the difference, since both of them use same technology?--18jahremädchen (talk) 00:18, 29 January 2008 (UTC)

The principles they operate under are similar, but they use far different methods of applying force. If you actually take the time to read the articles and compare the information you'll see that one uses a solenoid method and the other uses the following: "A wire (the projectile) carrying an electrical current, when in a magnetic field, experiences a force perpendicular to the direction of the current and the direction of the magnetic field." That was directly from the article by the way.--Oni Ookami AlfadorTalk|@ 01:50, 29 January 2008 (UTC)

## Um ablation of the rail?

Isn't one of the biggest problems with railguns the fact that you need to have a sliding contact that can carry massive current at hypersonic speeds, and so the rail tends to erode with each firing? The article seems strangely silent on this issue, but IRC it's probably the major problem.- (User) WolfKeeper (Talk) 18:40, 3 February 2008 (UTC)

I mean what use is a gun you can only fire a few times?- (User) WolfKeeper (Talk) 18:40, 3 February 2008 (UTC)

Find a source and then include it. Everything needs a source.--Oni Ookami AlfadorTalk|@ 23:58, 3 February 2008 (UTC)
Any developing technology will have limitations. The first rockets couldn't reach the Moon. The rate-of-fire of a flint-lock can't compare to a modern revolver. Historically, the development of the cannon included some colossal failures.
I agree that the article is vague concerning specific railgun design problems. The Office of Naval Research web site at http://www.onr.navy.mil/emrg/electromagnetic-railgun.asp has information about the issue of bore life, i.e., the effects of plasma ablation, arc and plasma erosion, hypervelocity gouging, etc. Check the ONR electromagnetic railgun briefing at the bottom of the page. On the other hand, in the interest of accuracy, might it be best to retain the article's general description of the problem rather than try to keep pace with the details of rapidly-changing developments in technology? Mtd2006 (talk) 17:27, 6 February 2008 (UTC)

I think a good solution to the rail ablation problem would be making the shell and the rails contactless by transmitting the electricity wirelessly. The technology is available; Nikolai Tesla came up with it over a century ago. Does anyone know if this would work? - TheJuggernaut10 (talk) 21:00, 20 July 2008 (UTC)

A contactless system is readily possible with a coilgun - almost by definition a railgun involves sliding contacts. — Preceding unsigned comment added by Knobeeoldben (talkcontribs) 18:52, 22 November 2012 (UTC)

## three or two? and sabot?

From the article: A railgun consists of three parallel metal rails (hence the name) connected to an electrical power supply. I only see two rails in the diagram.--Vidkun (talk) 14:35, 5 February 2008 (UTC)

I just watched the video that was released in the last week or so of the navy test shot - any speculation on what the sabot used for the KE penetrator was? I thought the shot had to have a conductive object in contact with the rails for the current to flow? from what I have found on the web looks like they use a combo: non-conductive disintegrating/discarding sabot and conductive discarding armature "plug" behind the sabot and penetrator--Vidkun (talk) 14:44, 5 February 2008 (UTC)

Per WP:NOT and WP:TALK, there is no point in speculating since it will not make it into the article. There are discussion forums for that.--Oni Ookami AlfadorTalk|@ 21:09, 5 February 2008 (UTC)

## Recoil as a design consideration

Speculation about the effect of recoil caused by the issues such as "firing an object of even minor mass at the high speeds railguns are intended for" is unsupported. The implication is that the velocity of a railgun projectile is a significant design constraint and it's unique to railguns. On the contrary, recoil is not unique problem in railgun design as the forces involved (as a result of recoil alone) are no different than existing projectile weapons.

There are two effects involved in recoil, momentum and energy (see physics of firearms). For momentum, a 20 kg railgun round traveling at mach 7 equates to a 12 mm/sec velocity of a 4,000 tonne naval vessel. Quoting from physics of firearms, "The ratio of the energies is the same as the ratio of the masses (and is independent of velocity)." While the velocity of a railgun round is high, its mass is insignificant compared to the railgun itself and its mount.

As stated under the Materials section, the unique design constraints for a railgun are dissipation of heat due to electrical current and friction, and repulsive forces on the rails. Specifically, several problems have been seen in railgun tests including: melt deposit, hypervelocity gouging, plasma and arc erosion of the rails; and joint damage, lamination cracks, and plasma erosion of the insulation separating the rails. Mtd2006 (talk) 16:32, 6 February 2008 (UTC)

## Magnetic field and current

Railguns use a sliding contact to pass a large electric current through the projectile or sabot, and this generates a strong magnetic field that accelerates the projectile.

There are conceptual problems with this description of a railgun. One problem is that it's too specific. A railgun can pass a current through a projectile or use a sliding contact.

No, there's always a sliding contact of some kind, since the projectile/armature/sabot/whatever is moving, and the current must go through it.- (User) WolfKeeper (Talk) 22:26, 6 February 2008 (UTC)
Current does not go through whatever is moving. Current flows from one rail to the other through a conductor between them. A railgun can be designed so that the projectile itself is the conductor, or alternatively, a separate conductor (a sliding contact -- not a unambiguous term) behind the projectile is the conductor. Indeed, the projectile might be a non-conducting material. Mtd2006 (talk) 08:03, 7 February 2008 (UTC)
If you draw a box around the moving portion, then the current inevitably penetrates that box, so yes, it does go through the moving part.- (User) WolfKeeper (Talk) 10:51, 7 February 2008 (UTC)

The purpose of a sliding contact (and a sabot) is to isolate the projectile from the current and thereby reduce heat generated in the projectile. But in either case, generally speaking, the interaction of a magnetic field and a current accelerates the projectile.

Depends how you define 'projectile'. Since the sabot is also projected, you may consider it to be part of the projectile. I've also seen it been described as armature.- (User) WolfKeeper (Talk) 22:26, 6 February 2008 (UTC)
I submit that the concept of a projectile from a gun is clearly understood. The fact that other stuff comes out of a gun does not make that other stuff a projectile in the context of a gun. For example, the sabot article assumes this distinction without lengthly, irrelevant discussion about the difference between "projected" sabot material and the projectile that it protects. Mtd2006 (talk) 08:03, 7 February 2008 (UTC)

Explanation:

1. As shown in the diagram in the article, the current in the rails generates the magnetic field that's used in a railgun. It's not the current in the projectile or sliding contact (the conductor between the rails) that generates the magnetic field.

That's a bit arguable, but I've already clarified that.- (User) WolfKeeper (Talk) 22:26, 6 February 2008 (UTC)
It isn't "arguable..." while any current produces a magnetic field, it's the current in the rails that produces the magnetic field. The current in the conductor interacts with the magnetic field to produce the force that accelerates the projectile. The force is Lorentz force which is the theoretical basis of the railgun. Mtd2006 (talk) 08:03, 7 February 2008 (UTC)

2. When a railgun uses a sliding contact, its purpose is to provide a conducting path between the rails. The sliding contact does not pass current through the projectile or the sabot. The purpose of the sabot is to guide the projectile between the rails and to isolate it from the current through the conductor. The conductor, in fact, acts as an electrical short between the rails.

Depends what you mean by projectile.- (User) WolfKeeper (Talk) 22:26, 6 February 2008 (UTC)
The common use of projectile in the context of a gun applies. There's no point in redefining projectile to include other stuff. Mtd2006 (talk) 08:03, 7 February 2008 (UTC)
The wikipedia defines a projectile as: "A projectile is any object propelled through space by the exertion of a force, which ceases after launch" which seems reasonable and would cover the sabot. You seem to be using the term 'projectile' as if it meant 'bullet', but the terms are different, although there is overlap (a bullet is a particular kind of projectile).- (User) WolfKeeper (Talk) 10:51, 7 February 2008 (UTC)

3. The Theory and construction section of the article explains the interaction of the magnetic field and the current in the conductor, but to clarify what's happening, the current in the rails generates the magnetic field, whereas the current in the conductor between the rails (perpendicular to the magnetic field) is the source of the force that produces the acceleration. As it happens, the same current that passes though the rails also passes through the conductor, but the effects are different in each of them. As stated, that's how it works.

'As it happens' is completely inaccurate. In all rail guns it is the same current, essentially by definition of what a railgun is, and how it works. If you are aware of a railgun where this is not the case, then I would appreciate a link to a paper describing this, as I am always interested in learning more or any subject.- (User) WolfKeeper (Talk) 22:26, 6 February 2008 (UTC)
I don't understand your remark. I think we said the same thing: that the same current that flows through the rails also flows through the conductor between them. In the rails, the current produces a magnetic field. In the conductor, the current interacts with the magnetic field, i.e., the purpose of the current through the conductor is to produce Lorentz force. There are different effects of the current in the rails and the conductor. Together, the magnetic field produced by current in the rails, and the force produced by the current through the conductor are the quintessential features of a railgun.
I just mean that the term 'as it happens' implies a degree coincidence, but if it wasn't the same current, then it wouldn't be a railgun, so there can be no coincidence at all; and this too is a quintessential feature as you put it.- (User) WolfKeeper (Talk) 10:51, 7 February 2008 (UTC)

There are a number of minor edits that might improve the article. For example, where the article says, "created magnetic field circulates around each conductor," it would be more precise to say "created magnetic field circulates around each rail."

Would it be useful to discuss some changes before revising the article? Mtd2006 (talk) 21:57, 6 February 2008 (UTC)

The previous introduction basically just said, something carrying a current is moved by a magnetic field in a projectile-like way. While this was not actually wrong, it completely failed to identify what a railgun is, and many other electromagnetic accelerators would meet that definition, without in any sense being railguns. For example a coilgun could use an active projectile with a coil in it, but this would still be a coilgun there being no rails, and a bore made of coils that would be sequentially activated, but the acceleration would be due to current in a wire; and according to the old definition of railgun, that would make it a railgun. No.- (User) WolfKeeper (Talk) 22:26, 6 February 2008 (UTC)
I agree. The original introduction did not make a clear distinction between a railgun and a coilgun. Other types of accelerator fit the description, but that's because a railgun is an accelerator. But as soon as we call this thing a railgun we've excluded the things called accelerators. What should be a concise description would be buried in the details needed to unambiguously define a railgun -- distinguishing it from hybrid technologies, accelerators, motors, motor-generators, etc. -- any device that uses current and a magnetic field to produce motion.
Okay, so how do we avoid too much detail that is better described in a Theory of Operation section, or information that's overly dependent on an specific implementation?
I suggest that the introductory description should avoid implementation details such as the use of a sabot or current through a projectile. Neither of those implementation details are necessary features of a railgun. Is it necessary to unambiguously define a railgun to describe it? Shouldn't the details of theory and implementation be left to the article? A simplified description won't unambiguously define a railgun, but it avoids redundancy and leads the reader to the details in the article. Mtd2006 (talk) 08:03, 7 February 2008 (UTC)
I agree that unnecessary implementation details should be avoided, but the necessary general principles need to be covered for identification purposes.

## Formula Units?

In the formula in the article what are the units (in particular, F)?

F is in Newtons. —Preceding unsigned comment added by 131.247.244.189 (talk) 21:38, 28 February 2008 (UTC)

Really? Because I ran some numbers through it (D=50 mm R=10 mm) and even with 500 amps it would only be 0.138629436 N. I might have the permeability constant wrong (4pi times 10 to the negative seventh?). —Preceding unsigned comment added by 66.245.148.237 (talk) 01:33, 3 March 2008 (UTC)

Reread the article carefully, and you will notice that railguns take current in the megaampere range. 500A is short of that by a factor of 2000. Square that again, and you will get very significant forces. Laschatzer (talk) 16:00, 21 May 2008 (UTC)

## Use in science fiction

You realise that Coilgun(gauss gun) is used more in Mecha than 'railgun' since it is used in such games as: MechCommander 1 & 2 MechAssault 1 & 2 and many other games and other forms of science fiction use it aswell, I only remember knowing that Red faction and the Quake series use it but I bet theres more.... RoflOhLol (talk) 14:12, 9 May 2008 (UTC)

I've moved all fictional references to Electromagnetic projectile devices (fiction)- (User) WolfKeeper (Talk) 22:58, 2 July 2008 (UTC)

## Induced EMF due to Faraday's Law?

In addition to the constant Lorentz force that propels the conductor along the rails, would not there be a retarding force that slows the conductor along the rails. When the sliding projectile moves along the rails, would not there be an induced EMF, as the magnetic flux given by $\phi = B.A$ increases with time?

From the equation of the total magnetic field given in the article, the EMF can be derived. The induced EMF is given by :$E = \frac{\mu_0 Iv}{ 2\pi d} \ln{ \frac{d-r}{r}}$.Where, the v is the velocity of the sliding conductor.

The lorentz force slowing the conductor is given by :$F = \frac{\mu_0 I^2 v B}{ 2\pi R} \ln{ \frac{d-r}{r}}$

where B is the magnetic field between the wires and R is the total resistance. Therefore as v increases the induced EMF and consequently the opposing Lorentz force increases as well. Am I getting something wrong? —Preceding unsigned comment added by CasperDude (talkcontribs) 16:56, 15 June 2009 (UTC)

## Picture of Railgun test firing

While cool and all, the picture of the Navy's January 2008 railgun test firing needs a caption explaining what is going on in the picture. To the average person, it looks like a normal gun with a fireball from burning propellant (and indeed that's what I see). I know this is not the case, though I'm clueless to what is happening (I had a hard enough time understanding how the railgun works). Alternatively, something could be put in the article body text explaining the effects of firing a railgun or something similar, or both a explanation in the caption and the article text. – Andrew Hampe Talk 05:36, 22 July 2009 (UTC)

## Removing Modern Mechanics cover picture

The Modern Mechanics picture (http://en.wikipedia.org/wiki/File:Electric_gun.jpg) is an artist's interpretation of a coil gun not a rail gun. Also, the one page article in that 1932 issue of Modern Mechanics was about coil guns, not rail guns. I am removing the picture.165.91.10.87 (talk) 06:48, 24 October 2009 (UTC)

## The other rail gun

No, I'm not talking of railraod guns; but of a Swivel gun -- those were sometimes also called rail guns in the 18th/19th century. Seegras (talk) 15:26, 13 February 2010 (UTC)

## Want to ride one?

Ok, so it's a little bit of a stretch, but "Superman: The Escape" at Six-Flags could be described as a rail-gun. Just dawned on my as I watched their ad about their new rides. For me, it just makes that ride cooler... 208.38.59.162 (talk) 20:34, 22 October 2010 (UTC)

Superman ride uses linear induction motors. Both are methods of electromagnetic acceleration, but they're not the same thing. Hock (talk) 17:42, 29 December 2010 (UTC)

## O.R.

"They gave the project the Latin motto "Velocitas Eradico", which they translate as "Speed Destroys" but can more accurately be translated "I am speed and I destroy," or similar."

The first part is fine, give the name of the project and the official translation. But where did the "more accurately be translated" part come from? As silly as it sounds, Wikipedia simply regurgitates information, we do not add or remove data unless we can cite official sources. Which going by some articles are popular culture magazines and some randoms geocities page. But even if you're citing using material that isn't worth the memory to display, that's still a cite. Simply saying 'I have a better translation, see?', isn't allowed. Make a geocities page and get your mate to post and cite it like everyone else. 220.235.43.42 (talk) 20:10, 10 April 2011 (UTC)

Fine. I'll use Perseus as my source, though... — Preceding unsigned comment added by Hellosparta (talkcontribs) 13:13, 11 June 2012 (UTC)

Also, what is currently says is untrue: "The motto is currently under debate in the railgun community and among Latin scholars." The source given shows an OP who makes a simple mistake; a subsequent post corrects him, and he admits he was mistaken. I don't see any debate there...Hellosparta (talk) 13:20, 11 June 2012 (UTC)

If I remember my Latin, "Velocitas Eradico" means "I kill velocity", not "Velocity kills (something)". Just my 2p. 57.250.245.249 (talk) 16:19, 13 May 2013 (UTC)

I'm surprised no one's said it yet: "Speed Kills" — Preceding unsigned comment added by 68.61.164.169 (talk) 19:29, 25 May 2014 (UTC)

I'm sure the authors of the motto meant something like "speed kills" but they seem to have ended up with something much more like "I, speed, eradicate". Having cool mottos for railgun projects is nice but making significant technical advances is a much better way to earn the respect of one's peers and sponsors. — Preceding unsigned comment added by Knobeeoldben (talkcontribs) 09:36, 6 April 2015 (UTC)

## US Navy test 2011/11/2

Since nobody else has posted this here, I'll add this: [[2]]

Hopefully someone will be able to add a reference to the source report (Physics). L0ngpar1sh (talk) 22:34, 7 November 2011 (UTC)

## Flame/plasma plume

Some IP users keep changing flame plume to plasma plume. This is wrong, as the citation I provided states, it's a flame plume. It would be nice for other users to keep an eye out for these people who keep reverting to the completely uncited claim that the plume is plasma. ScienceApe (talk) 00:53, 6 November 2012 (UTC)

The word "plasma" has long been adopted by the railgun community but it is used in a very loose sense. The "switchgear" term "arc" is probably a lot more appropriate for the typical state of ionisation and temperature in a railgun "plasma armature". "Muzzle flash" or "muzzle arc" might be less controversial terms for the luminous cloud of "smoke" that comes from the muzzle - especially where the launch has used a solid armature. The term "flame" infers that combustion is a significant process therein and that in turn requires a significant availability of oxygen. I think much of the physics of candle and gas flames will apply here too. I seem to recall that the most visible "yellow" part of a flame is the combustion products cooling post-combustion, so perhaps ablated/eroded railgun bore and armature materials cooling post shot will give the same appearance whether or not much oxidation has actually taken place. 06.11.2012. — Preceding unsigned comment added by 82.132.210.73 (talk) 08:29, 6 November 2012 (UTC)

Flame is just a hot gas that radiates due to black body radiation, nothing actually has to be "combusting" the gas just needs to be hot. But in this case, it seems the projectile is made out of aluminum and bits of it are disintegrating off and burning in the atmosphere, producing flame. ScienceApe (talk) 18:02, 17 November 2012 (UTC)

Having once been lucky enough to watch the test firing of the Maxwell Labs 9MJ SSG railgun, there was certainly a lot of "muzzle flash" on that occasion, much like in the linked video clip. However we were also told at the time that the degree of muzzle flash was significantly less than would be expected from a conventional gun of an equivalent size.Knobeeoldben (talk) 21:16, 6 November 2012 (UTC)

The Maxwell 9MJ SSG only used "plasma armatures" but the competing CEM-UT 9MJ SSG programme included a lot of work to develop fairly reliable solid armatures - typically fabricated from aluminium alloy. Even with a perfect "transition free" launch, there will most likely be a significant muzzle arc, so in a single shot railgun a lot of the residual stored magnetic energy will just dissipate in the arc.

I expect that the latest US Navy railguns use solid armatures developed from the original SSG designs. In the 1990's there was a lot of thinking that proper long range "tactical" projectiles might not include the armature mass, so that the armature and some sabot components would be discard soon after launch, leaving a more aerodynamic, sub calibre munition as the "flight vehicle". Knobeeoldben (talk) 18:47, 22 November 2012 (UTC)

## Possible Math Error?

In the section "Railgun design", subsection "Mathematical Formula", the article claims that we can calculate the average magnetic field between the rails by integrating the field then dividing by 2d. Unless I'm missing something, the division should only be by d, not 2d. Any thoughts? — Preceding unsigned comment added by 134.10.130.173 (talk) 07:34, 8 March 2013 (UTC)

If formulae for infinitely long conductors are used, then the factor of 0.5 (1/2) is needed to correct the field, because the conductors in railgun are not infinite. In effect they run back from the armature towards -infinity but, when there is no current forward of the armature, you only get half the field predicted from an "infinite wire" formulation.Knobeeoldben (talk) 15:21, 17 March 2013 (UTC)

Knobeeoldben (talk) 17:59, 17 February 2014 (UTC)== "recoil force not explained by the modern electrodynamics" ==

Materials used is contradictory, defending scientific understanding of stresses, even including citations, but then affirms there is no such understanding: "However, the recoil force acting along the rails cannot be explained by the modern electrodynamics: the is no force acting along the conductor with electrical current in the modern physics. It is therefore necessary to consider the scalar magnetic field." Is there anyone else who can confirm this? Skarmenadius (talk) 18:34, 12 February 2014 (UTC)

My understanding is that there is no axial force recoil force along the rails. If you analyse a railgun using the obsolete Ampere force law, then that will predict axial forces on the rails. If, instead, you apply a more conventional analylsis using the Lorentz force law you will get the conventional result that the recoil force appears on the breech closure.

I added the various references from Bill Weldon and the likes of Michael Putnam a while ago to show that those involved in practical railgun work generally do not accept the validity of the deductions from the Ampere force law. As far as I know, Neil and Peter Graneau were the original "champions" of the Ampere force law in the sphere of railguns and they published a number of papers and articles c.1990 setting out their views. At that time, John Allen, an academic from Oxford University (UK) took it on himself to challenge their position via journals such as the AIP Journal of Applied Physics. Essentially, work published by Page and Adams in 1945 ("Action and Reaction between moving charges", Am J Phys 13, 141) is cited by Bleaney and Bleaney (in their book Electricity & Magnetism) as the way to explain things like railgun recoil without recourse to empirical means such as Ampere's law.

In the 1990s most research railguns were so heavy that the accomdation of recoil forces was not really a practical problem. Quite a lot of work was done then to compute accurate three dimensional rail and armature current distrubutions for railguns - if anything typical results from those studies would suggestion that some secong order axial forces might be exterted on the rails near the armature - but in the same direction as the force on the projectile.

It is interesting to see that this "interesting debate" is still going strong twenty years later. My personal view is that challenges and debates like this should be tolerated for their educational merits. The physics can get quite complicated, if you do not always analyse a closed loop of current. If you analyse a closed loop of current, then both force laws predict the magnitude of the projectile force and recoil correctly. Knobeeoldben (talk) 17:59, 17 February 2014 (UTC)

## Bad assumptions re: power needed

(1) Nuclear powered ships do not produce more power than conventionally powered ships. The difference is in how long the fuel lasts. (2) Railguns needs lots of electrical power. Conventional ships have lots of conventional power, but this power is mechanically coupled to the screws, and most ships have only small electical generators. (3) The American DDG-1000 Zumwalt class and the British Type-45 Daring class have integrated electrical power. (Also: some historical US battleships. also: the Ford class carrier.) Their main gas turbine power plants drive electrical generators, which in turn drive electric motors on the screws. This electrical power would also be available for other uses, e.g. future railguns. (4) Nuclear power plants are generally very unresponsive to changes in demand - unlike gas turbines - so in fact a nuclear powered ship would be less suitable than a gas turbine powered ship, for powering electric weapons. 81.96.58.117 (talk) 23:25, 11 May 2014 (UTC)

Providing suitable sources of prime power has always been a challenge for potential military applications of Railguns. If the "weapons platform" in question has an integrated electrical power system, then it ideally needs to have the power rating to supply main propulsion power AND the needs of any weapons systems concurrently, even if this is only a short term "intermittent" rating. I have not encountered too many military commanders who would be very happy about having to wind down their propulsion system in order to fire their main weapon(s). Knobeeoldben (talk) 19:12, 14 May 2014 (UTC)

They would not have to stop the ship to fire. Ships generally operate according to the 1/3rds rule, whereby 1/3 of the power will move the ship at 2/3 of the speed. So a DDG-1000 or Type-45 would drop from 30 kt to ~25 kt whilst firing. Having a load of extra generators to ensure the full speed is a lot of money for not much effect, 81.96.58.117 (talk) 22:53, 17 May 2014 (UTC)

That certainly would not be a problem if using a railgun as an offensive weapon, e.g. as in litoral warfare. I'm less convinced about the merits of this for defensive uses of the armament though. If you are facing inbound threats then compromising the ability to change direction or speed could be a significant dis-benefit.

If you have railgun that needs ~50MJ per shot and a firing rate of 6 rounds per minute is acceptable then the average power is 5MW. That is certainly in the right ballpark for the output from a naval gas turbine generator. Knobeeoldben (talk) 09:56, 18 May 2014 (UTC)

I've just added a citation request to "and the faster it is removed, the more heat is generated. [citation needed]" because that seems counter-intuitive to me!

In the absence of any further techincal input I have attempted to close iut my own query. In passing, I note the point about extraction/ejection is probably a bit of a red herring - most big guns now fire caseless ammunition. I'll see if I can think of an elegant way of correcting that... — Preceding unsigned comment added by Knobeeoldben (talkcontribs) 09:51, 11 October 2014 (UTC)

## U.S. Navy tests

The subsection "U.S. Navy tests" header was placed directly below several paragraphs about U.S. Navy tests. Odd. These paragraphs contained nothing but information about Navy tests. So I move the header to just above them. Nick Beeson (talk) 11:53, 15 June 2014 (UTC)