SpudFiles

Your question was; is it worth it.
I think it might just not be..

You need to go through a lot of trouble to end up with an expensive awkard thing that will only be fun to shoot like 5 times.

It's more fun thinking about it...

Hi,

You could also consider evacuating the barrel in front of the projectile... of course you will need some cover at the muzzle, like a union with a burst disk that is good for just 1 bar (it will be shot through directly by the projectile). And some near vacuum pump. Just an idea.

Hmm, wonder whar the sonic speed is for the HOT combustion products of oxygen and propane? Even after a decompression (with temparature drop) it should be nice and high.

Regards
Soren

In a hybrid chamber after combustion, the speed of sound is roughly equivalent to the speed of sound in room temperature helium, as far as I know.

@BTB: I kind of thought of that already. It would be more just to know that you did it than anything, and for bragging rights of course. The most fun guns of all are the reasonably high powered hand held ones, not the monstrous and awkard super-powerful ones. Kind of like what you build, actually.

I would never build my own steel chamber from pipe for this, too expensive defiantly use an existing air tank, remember with unregulated helium its going to be really expensive for every shot and you'll probably rarely use the gun because of that, so don't waist too much money on this

I think its a very good idea indeed to place a burst disk next to the ball valve.
Maybe you can create a burst disk of thick sheet PVC or other very sturty material.

Oooooooooooooooohhhhhhhhhhhhhh........
OK, helium-powered marble machine gun!!!!

An existing air tank wouldn't have a wide enough opening, as the valve would have a 1" diameter port. The pipe wouldn't really be that expensive either.

It would be really expensive for every shot, but I probably won't even build this unless I can't get my burst disk gun working, which is also rather expensive to shoot (and time consuming).

This whole thing is purely hypothetical so far, because if I can't find a way to get parts from the US, it won't be possible.

If your using helium and are prepared for awkwardness, just to bragg, might as well figure out a piston to shock-heat it..

One oversized "springpiston"cannon that uses a gigantuous T valved cannon as the spring..All filled with helium of course..
use a burstdisk between the piston and the barrel..

Yeah, made out of SCH 80 seamless SS. The kinetic energy of the piston would allow it to compress the helium in front of it to 3000+ psi if it was going quickly enough and was heavy enough. Then you just need to figure out how to stop the piston from completely destroying the backstop when it hits. I could see that exceeding Mach 3 easily, but it pretty much throws out the original idea of a SIMPLE and relatively CHEAP launcher that can exceed Mach 1, doesn't it?

Marco321 wrote:Will it really reach mach 2? What I'm getting at is will the helium be able to expand fast enough to reach like 460m/s? A golf ball will have alot of drag so it will be even harder.

But none the less it will be very cool. i hope you make it lol.

If you are concerned about the chamber, why not use a helium tank as the chamber, it may be a little expensive, but you will be able to have full confidence in it holding.

I used a medical oxygen tank--size "E". Rated for 2,000 psi working pressure. Really cheap on ebay. Got mine for 12 buck delivered.