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CO2 tank hybrid, question about fittings.

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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CO2 tank hybrid, question about fittings.

Unread postAuthor: pyrogeek » Sun Aug 12, 2007 12:54 am

After building a couple combustions, a pneumatic and a few minis, I am looking at finally getting into hybrids...partially so I can go to school and say I own a hybrid. Also the idea of supersonic potatos intrigues me.

I have a 5lb CO2 tank, and a 10lb tank. Both are rated to 1800PSI. Neither have very large holes in them for pipes, and I don't think they are standard threads anyway. The 5lb probably has a fitting for about a 1/2inch pipe, and the 10lb has a fitting for probably a 1inch fitting.

My question is, would it be safe to cut the tank and weld on a larger pipe fitting? it's thick metal, but I have a hacksaw and hours of spare time, as well as a cutting torch at my disposal. I have access to a nice MIG welder, and can weld pretty well. Actually, very well, to be quite honest.

Also, how large of diameter barrel should I have compared to the tank size? Is there any rules of thumb or calculations to find what is safe?



This is a bit off topic, but has anyone here heard of Tannerite? It's a type of commercially available target that when shot with a supersonic round, it detonates. How hard would it be to keep a round going supersonic for, say, 75yards to set this stuff off?
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Unread postAuthor: frankrede » Sun Aug 12, 2007 1:17 am

I think it would detonate using a metallic projectile with a pointed tip.

I think it would be safe using a co2 tank and welding a fitting onto it. You would have to do all your tests up to 6x remote with expectancy to blow to test it, if it survives it should be good

edit: Sounds like a great idea and I can't wait to see it
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Unread postAuthor: pyrogeek » Sun Aug 12, 2007 2:39 am

My plan is to taper both pieces (tank and fitting) at about a 60 degree angle before welding, and then I'll lay down 3 or 4 welds overlapping each other. I should get great penetration that way, and as strong of a weld as possible.

What kind of ratio should I use for the tank volume to barrel diameter? Like, I wouldn't put a .177 barrel on a huge combustion. Or should I just go big and slowly get smaller barrels?
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Unread postAuthor: frankrede » Sun Aug 12, 2007 2:49 am

I would say with a big chamber your standard barrel should be as big as your valve is.
But keep a variety, a little choke isn't that bad, and with a tiny barrel just compensate by making it long(LOL)
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Unread postAuthor: pyrogeek » Sun Aug 12, 2007 12:31 pm

Well of course you want the valve as big as the barrel (or bigger). But, the tank is maybe 18inches tall, 4inches wide (just rough estimates). Figure in about 1/4in walls. That would be like 120 cubic inches. Lets say feeding that through a 1inch barrel?
Purely for safety reasons, I don't want to go larger than necessary since the fittings can't hold as much as you go smaller. But I don't want to go too small either.
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Unread postAuthor: beebs111 » Sun Aug 12, 2007 2:36 pm

with a hybrid and a large bore projectile, it shouldn't be too tough to detonate one of those exploding targets. if im not mistaken they're jsut ammonium nitrate mixed with high mesh Al to sensitize it. if you are really aching for an exploding target for your hybrid, they(you)can make more sensitive targets with some degree of know-how. potassium chlorate+german dark Al makes quite the sensitive flash powder.
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Unread postAuthor: pyrogeek » Mon Aug 13, 2007 4:52 am

Yes, that is basicly what Tannerite is. Ammonium nitrate, ammonium chlorate, aluminum and a small amount of something zirconium. ...don't ask. And no, I don't want to make something more sensitive. I'm getting a .223 rifle soon, essentially as soon as it can get ordered.
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