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Billybobjoe

Fri Jun 27 2008, 02:17AM

Registered Member #396 Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176

I would recommend concentrating on the speed of which your valve opens instead of the gas being used. Theoretically helium (well hydrogen but good luck getting that at high pressures) is the idea gas for this and the speed of sound in helium is lower, CO2 has a higher molar mass so, theoretically, that will affect projectile speed but this won't be as big of a factor as the valve speed. For practical purposes compressed air is suitable and launchers have been constructed that have broken the sound barrier. Really the point here is to have the the railgun accelerate the projectile so we don't really need it that fast (although it certainly will help).

rp181

Fri Jun 27 2008, 02:12PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

look into the "burst disc" method, its the fastest valve.

Bust_A_Cap

Fri Jun 27 2008, 02:23PM

Registered Member #1561 Joined: Mon Jun 23 2008, 07:58PM
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Posts: 25

so although gun powder is what came to mind first, what about any other contatined explosion? perhaps lighting the helium gas, and using this explosion to power the intial propulsion?

Hon1nbo

Fri Jun 27 2008, 04:50PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

Bust_A_Cap wrote ...

so although gun powder is what came to mind first, what about any other contatined explosion? perhaps lighting the helium gas, and using this explosion to power the intial propulsion?

you mean hydrogen (helium isn't flammable as far as I know)?... that would make water, and would be fine if there were no contaminants that would cause the water produced to be conductive (could cause a short, unless there is no chance of it getting around the projectile as if it doesn't the rails will fire fine, but must be dried)

Bust_A_Cap

Fri Jun 27 2008, 07:51PM

Registered Member #1561 Joined: Mon Jun 23 2008, 07:58PM
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Posts: 25

Again as far as the contaminents go, I'd liek to pretend that they aren't going to effect it because although they will effect it, you can make a system work around it, such as putting a false barrel in the beginning, one that isn't part of the railgun, and it could have holes cut in the sides to let any contaminents out as the bullet flew past.

As far as the mix up with hydrogen and helium, I meant to say hydrogen not helium, thanks for the correction DaJJHman

Hon1nbo

Fri Jun 27 2008, 08:06PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

Bust_A_Cap wrote ...

Again as far as the contaminents go, I'd liek to pretend that they aren't going to effect it because although they will effect it, you can make a system work around it, such as putting a false barrel in the beginning, one that isn't part of the railgun, and it could have holes cut in the sides to let any contaminents out as the bullet flew past.

As far as the mix up with hydrogen and helium, I meant to say hydrogen not helium, thanks for the correction DaJJHman

putting a middleman barrel sounds like a pretty good idea... as long as the projectile gets to the desired velocity before ports are used... also, if ports are used, that would allow for gasses that are normally undesirable since they can escape...

ArcLight

Sat Jun 28 2008, 05:51AM

Registered Member #341 Joined: Thu Mar 23 2006, 07:41PM
Location: Northern Illinois, USA
Posts: 69

I have a conversion kit that allows me to shoot .177 caliber pellets out of a .38/.357 revolver using only large-pistol/large-pistol-magnum primers for propellant. The pellets really come whistling out, but just one cylinder-full makes the weapon filthy.

If I were in your position, I would seriously consider using compressed air. I routinely launch 29 grain, .22 caliber lead projectiles at over 1100' per second down an 18â€ barrel using only air for the propellant (you can ask the surviving ground squirrel population if you can find any.) Clean/filtered air is conveniently packaged in various sized containers (80 cubic foot being the most common) at 3000 PSI from any dive shop for just a few dollars.

Fittings, adapters, and valves can be obtained from custom air rifle manufacturers.

Regards, ArcLight

ea6b607

Sat Jun 28 2008, 07:07PM

Registered Member #1320 Joined: Sat Feb 16 2008, 01:31AM
Location:
Posts: 67

I used just plain old CO2 for mine did the calculations for expanding gas and it was about 80% efficient. The key as someone already mentioned is to empty that gas as fast as possible. For mine I used 1 $150 3/8" fast open high pressure DEMA valve I bought locally and it can empty a 12oz CO2 tank in about 2 second when directly connected. Honestly if your just going to use a rifle round any extra speed your going to get from the rail gun is going to be pretty negligable unless you have a pretty big capacitor bank. Also injection doesn't really help with efficiency, it's still exposed to the same magnetic forces for the same amount of time with the same friction, although it does spread out the rail erosion.

ramses

Wed Jul 30 2008, 04:03PM

Registered Member #1208 Joined: Thu Jan 03 2008, 05:30PM
Location: Chesterland, OH
Posts: 154

Here is a calculator designed for pneumatic potato guns, and it it proven to be somewhat accurate. I am surprised that rp181 hasn't posted it yet.

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