SpudFiles

Okay, reiterating what Mark said: some people here have a very, very inflated opinion of how powerful this would be. Schedule 80 steel pipe and fittings are RATED for roughly 3000 psi, meaning that their failure pressure would be around 9k. Schedule 160 pipe and fittings are usually rated in the 6kpsi range. They are also DAMNED HEAVY. My 2" SCH 80 steel union weighs about 7 pounds by itself.

To put recoil, and a few other things in perspective: Even with a 12' long 2" SCH 80 barrel (which would be terribly heavy and unwieldy), this thing would barely be topping Mach 1 with a 500g load, assuming that it could even overcome trans-sonic flow effects (which is quite possible considering the relatively high pressure). This would give a muzzle energy of 26k ft/lbs, by a very liberal approximation. The Mythbusters' "Old Moses" 3.5" bore cannon fired 8 pounds at Mach 1.5, and just incase you didn't notice, the operators weren't horribly killed by it. If recoil becomes a problem, just add weights to the cannon, or beef up the supports.

My ME20H-41 does 10k ft/lbs and weighs a tiny 50 pounds, and it only kicks back 3 feet or so without any brace whatsoever.

As for a barrel: Suprisingly enough, I made a barrel that survived several shock loads of up to 2000psi by sleeving 1.5" ABS pipe inside 3" ABS pipe, and filling the space with structural fiberglass. If you want to go the non-ghetto way, and are prepared to sell the soul of your firstborn to UPS, you could get a SCH 80 steel pipe shipped to you from McMaster-Carr.

you would get a metal stand with car shocks and and electronic egnition system i may be crazy but i am not dumb

Wait, is this going to be a pneumatic, or a hybrid? Because I have to say, if you plan on trying a 3kpsi pre-ignition hybrid in a SCUBA tank:
1. Propane/air liquifies at ~190x, well below 3kpsi.
2. If you do it, by using hydrogen or something, the tank will be ripped to shreds, and so will all of your expensive fittings, and anything within 10 feet of this thing when it goes off.

lol some suggest pistons, some suggest solenoid valves..

hell if you really want power do a burst disk... you will only need about 5000 layers of aluminum foil. lol

Actually, in a 2" SCH 80 union you'd only need about 350 layers of standard household alu. foil to easily hold back 3000psi.

Nonetheless, a burst disk valve wouldn't be practical for a design like this in most cases.

I think it would be a great project, if anyone could afford to build it properly. If I were to build it I would use a piston valve (piloted by the high pressure solenoid mentioned) housed in a custom machined "tee" and everything would be bolted together like steam pipe. I would probably want to use steam or hydraulic tubing for the chamber and barrel. I would only fill the cannon from the scuba tank as well. All this is assuming you want to make it in 1" caliber or bigger. If it were smaller I would go in a completely different direction.

I'm in a welding course and I've seen a full cylinder (about 3600 psi) of argon fall over and snap the top off. It didn't go anywhere, it just lay there and all that was stopping it was a cable on the ground from the welder. It took about 15 seconds for the whole tank to empty and it wasn't really that loud. It could have been bad but it wasn't. To be dangerous the tank would have needed space to start accelerating. Of course, if it was a cannon discharging, at that pressure, I would definitely expect a bit more movement, lol.

I've seen a full cylinder (about 3600 psi) of argon

What gas supply company do you use? The only pressures I've ever seen for argon tanks were: 2000psi (high purity for research) 2200-2600psi (various sizes of standard cylinders) and 3500 psi (high pressure cylinders with oddball threads that have to be adapted to fit anything useful). Most welding regulators are only rated for an input pressure of 3000psi, so you must have a pretty advanced setup there.

If you know where to shop, 6000 psi can be had.

(No, I don't know where to shop... I just know that I've seen racks full of 6000 psi bottles.)

Yea...I'm pretty sure everyone caught this but ignored it, but he posted in an old topic...I'm from NerfHaven, and the rules are a bit different there, so I'm not sure. Anyways, back on topic. I think 3000 is not that crazy, I'm a little more crazy than that. I'd say 9999 psi. Just kidding, probably two times that which is 6000 just like what the guy before me said. What exactly are you going to be using as the ammo? Please say a smartcar. And just out of curiosity, would this break the sound barrier? A supersonic spud gun? That is pretty awesome. So yea, shoot a smartcar...

No, the same thing applies here...Digging up a 2 year old topic to say something of no importance is heracy too, it's just been ignored in this case.

Yes, it would probably break the sound barrier, given the correct conditions and projectile.

ill bet you that 3000 psi rated pipe wouldn't break until at least 10000 they way under rate them otherwise if it was at 2999 and it failed they would get sued all the time

make a steam gun out of those pipes!