We are talkin about rail guns right !!!  Correct me if im wrong but Rail guns fire TINY aluminium rounds. At or near the speed of sound. There fore why the need for extra large storage.

Ammo size- for an orbital-scale Railgun, rounds ~4-8" in diameter would be appropriate. Especially in reference to the massive sizes of enemy warships.

Ammo type- aluminum would melt from heat ablation. Tungsten is actually the projectile of choice. Depending on the speed of the launch, it may need to be carbon-coated for heat resistance.

Velocity- the speed of sound at Earth's sea level is ~340 m/s. To get an idea of how SLOW that is, most modern firearms fire projectiles at around 600-1100 m/s muzzle velocities. Railguns, on the other hand, fire projectiles much faster. The current fastest projectile launch is a US Navy 90mm Railgun, which fired a slug with the energy of around 32 MJ (I think, I may have to recheck), and a velocity of 2520 m/s. Thats a little more than 1.5 MILES PER SECOND.

However, these defense guns are also intended for LONG TERM ENDURANCE. Hence, A LOT OF AMMO AND POWER STORAGE would be needed. Especially if these things are firing slugs real fast, like ~5000 m/s+.

the navys rail gun fire aluminim rounds could be wrong but pretty sure .

I think that your wrong, as aluminum hasn't been used for projectiles, well, since ever. Back in the Revolutionary/Civil War eras, it was lead. WWI-II, it was usually lead jacketed in copper. Now, it's usually armor-piercing steel rounds. Aluminum is sometimes used for conventional ammo casings, but NEVER for actually projectiles.

There's also the issue of heat stresses. Aluminum melts REALLY EASY. I mean it. It's also much less dense. For a modern armor-piercing anti-tank weapon system, you need something dense (i.e. HEAVY, more energy to it) and for a Railgun you need something to withstand a TON of heat. As such, Tungsten (or Titanium, though Tungsten is preferable) is the most optimal metal to use. It is the metal with the HIGHEST melting point, it is also very dense, so it is an optimal armor-piercing projectile.

If you use Tungsten but still need additional heat protection, coat it in carbon. But overall, aluminum wouldn't be used.

5000 miles per hour? Let me see, hmm, that's ~27.78 miles per second, which isn't feasible with todays current technology. The USN's current record is a projectile weighing 9 lbs, launched at the velocity of 2520 m/s (~2.5 m/s, which is ~=1.5 miles/second), with an energy of ~32 MJ.

It may be infeasible to you but the record set for a railgun round by the U.S. navy was 5,640 miles per hour.

http://gizmodo.com/351467/navy-rail-gun-test-destroys-everything-it-touches-at-5640-mph

if you would like to watch the video.

NOTE: The speed you quoted at 1.5 miles per second is the same as the speed I quoted of over 5000 miles per hour. Perhaps you converted miles per hour to miles per second incorrectly?

I stand corrected, as I did the math on it just now. Also, 2520 m/s is slightly FASTER than 8270 ft/s. Thus, the weapon is powerful.

Note:  Friction is not a problem in space.  The loss from heat will be significantly less when you take travel through atmosphere out of the equation.  A tungsten coated aluminium(a vastly abundant resource, unlike tungsten) shell would be just as able to survive the travel through the barrel, and be extensively damaging on impact.  At that speed, you get plasma, not a penetrating chunk of metal.  A heavier round would simply mean more power to expell it, space removes yet another problem, aluminium travels just as well as lead when you take the atmosphere out of the equation.

It's entirely logical for space based rail gun implementations to use aluminium.

i realise ammo is needed... i said in Sins we dont care about ammo... not that Railguns dont use ammo...

the comment about not caring about ammo is because by the same token Vasari Phase Missiles and TEC Missiles and AutoCannons never need reloading... for instance how does a little TEC or Vasari Fighter or Bomber remain useful in combat hours after being deployed from its hangar without needing to dock to reload its weapons...

Its simply a visual thing, but the design could use some more body... its just a little... whispy and unrealistic atm... but the general design is still cool

as for the science of railguns, i think thats pretty much been answered so...

just a note on your note... depending on the details, its possible the aluminium could melt from the electric current that travels through it in order to generate the magnetic force that makes a railgun what it is...

all it would take is a tiny flaw that would cause current and heat to build up in the slug and *problems*

im not saying its inherently a problem, but its very risky.... like underwater electronics... we can make it work, but one little failure or flaw and *problems*

I disagree with aluminum. While it's possible to MAKE it work, it is entirely sub-optimal. Tungsten is much more preferable, because it's denser, which will give it more energy in flight (more penetrative power), and also sturdier. Aluminum is too easily destroyable/meltable. It would likely just hit and crumple.

Tungsten on the other hand would not. With heat, coating Aluminum in CARBON (not Tungsten), would be more cost-effective. Additionally, Tungsten is one of the #1 armor-penetrating rounds used in heavy cannon (90mm+ bore diameter), possibly only superseded by depleted uranium (DU).

@Whiskey, i think people mean to say the slug would be Tungsten wrapped in Aluminium... Aluminium by itself would just crumple against a hard target, especially in space as the lack of friction wouldnt heat the aluminium so youve basically shot a coke can at a tank. thats the whole idea of magnetic acceleration weaponry, it takes something hard and propels it at such speed as to make it penetrate (And hopefully destroy or disable) the target.

Aluminium by its lonesome wouldnt do that. Tungsten, DU or even Titanium (though thats very expensive) would be better choices...

so basically, i agree with you, but i just wanted to point out i dont believe people are saying Aluminium rounds as in pure Aluminium...

ah, I see. Titanium is actually not as good as you'd think. It's good for combining w/ ceramics for armor, but not as good as a AP weapon. DU is by far the most optimal one, but for a magnetic-acceleration weapon Tungsten would be the optimal choice.

I say that because I am unsure as to how conductive DU is.

i would like to take this opportunity to get back on topic...

agreed.

Well not soo fast. I may remind that in spacee thing moving very fast have a lot of energy but ill give a good exemple a microasteroid made of simple rock travelling extremly fast  in sapce would just go right thru a space station like if it wasnt there infact i rmemberr one of the stargate episode the showed a microasteroid going right thru Radek and Atlnatis's walls.

Soo.. very possibly acording to einstien a shell made of alluminium travelling very fast could do more then what we could predict based off whatr we could predict here on earth 

Now we can go back too topic  riser's railgun  does it really have to fire metal why not plasma or laser bolts or chicken like in the mythbuster episode  

 Akkan117 

because the definition of a Railgun is that it fires a dense metal slug, and because if it fired plasma then it would be a plasma cannon, and if it fired laser bolts (wtf? what is a laser 'bolt'?) then it would be a laser, not a railgun

hence, why it fires metal slugs.

Fail.

as for whether aluminium would be able to penetrate a shield or hull if moving fast enough, thats true, but a railgun, especially a modern human railgun which isnt all that powerful relatively speaking, would not be able to propel the slug fast enough. micro asteroid damage is caused by small pieces of stellar debris travelling at a significat percentage of the speed of light (or alternatively, being run into by an object travelling at a significant percentage of the speed of light) and THAT is when the damage is caused. if you are travelling at that speed, then a feather or a tooth or a Daddy Long Legs spider could kill you/do damage. However, the slower the projectile or target is travelling, the harder/more dense the slug needs to be to do damage. As such, an aluminium slug travelling at anything less that a percentage of light speed would just crumple. it may give the shields a hard pinch, but they would recover pretty easily.

The real reason for using a railgun is to be able to fire anything thats what makes so special and for those like me who play eve online we no that we can fire alot of variety of projectiles which ranges from anitmatter charge , uranium to fusion charge (or plasma) even emp charges the railgun can fire anything that u want as llong as you can magneticly charge it there for my statement of lauching plasma (perhasp not lasers or chickens) was correct. Of cousre this is all theory we have yet to test using such materials in railguns and according to the stargate timeline we arent there yet so i guess we stick with metal slugs for now  .

Akkan117

Evening All,

I have spent some time over the last few days on about 6 different concepts, this is what we have chosen. It's based on parts of midway and the gun outside the Icarus base from the upcoming Stargate Universe. There is now enough space for ammo, power generators and so.

Enjoy

http://riser38.deviantart.com/

Just a quick update on where we are with the Tau'ri

Download Tauri.htm

I like the new one. It looks much nicer than the 2nd try.

abso-freaking-loutely! fantast job Riser, my faith in you is restored!

keep it up

looks awesome now ...

good job!!!!!!