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I have been a big fan of pneumatic cannons for a long time, for me a decent cannon was air powered, and all my cannons were air powered, pneumatics are powerful ,reliable, etc but I have to say they are not very practical when you want to leave you suburb and go shooting outside with your overpowerful cannon, you have to bring your pump or use a HP cylinder, if you're not lucky there is a stupid leak, a piston which jams due to a lack of lubricant, or a random issue you are unable to fix without proper tools, after two shots you are bored to reload with the pump, and you come back.
So I want something powerful, not needing too much pumping to reload, and easy to carry, hybrid could be an option, but they are a bit complicated, a reliable lighting seems to be a mess to make (no cheap tazer in France and i'm not fond of electronic stuff).
I think I will make a combustion cannon out of galvanised pipe and boost it with oxygen :
-Has anyone amongst you ever tried something similar ?
-Can I get a decent power (about the same power as a 10bar pneumatic with the same volume) at atmospheric pressure using butan and oxygen in a 2" chamber 50cm long ?
-Do you know a good "recipe" based on volume for an explosive mix of butan/oxygen at atmospheric pressure ? (the explosive concentration in air is 5% of butan, there is 20% of oxygen in air, oxygen has 5 times more oxygen than air, so 25%of butan and 75% of oxygen is good ?)

I would not be messing around with oxygen if I were you.

Here are some scary pictures of airguns that were filled with oxygen to convince you:









Hybrids really are no big deal, and you don't need a high energy source for ignition - I fired most of time using a small piezo ignitor from a common cigarette lighter.

Have a read through this thread: http://www.spudfiles.com/hybrid-cannons/topic21655.html

Damn, it's scary
That's a big issue if oxygen is so dangerous, but those airguns were using HP, you think it could detonate even at atmospheric pressure causing a DTT ?
The problem with hybrids is that we have to use a burst disk and replace it on each shot, or use a piston which is hard to make without proper tools, and the piston design is less compact.
Your piezo could ignite up to which mix ?

Brice wrote:Damn, it's scary
That's a big issue if oxygen is so dangerous, but those airguns were using HP, you think it could detonate even at atmospheric pressure causing a DTT ?

Concentrated oxygen makes things burn that normally wouldn't, even if at atmospheric pressure.

The problem with hybrids is that we have to use a burst disk and replace it on each shot, or use a piston which is hard to make without proper tools, and the piston design is less compact.

I can see the appeal, I thought about this a while ago as an easy way to make cartridges: http://www.spudfiles.com/hybrid-cannons/topic17788.html - in the end I gave up on it because it was too much trouble to source the oxygen.

Your piezo could ignite up to which mix ?

Up to 16x reliably, the crucial factor is making the spark gap as small as possible - the thickness of a sheet of paper - if you want to go for higher mixes.