One possible solution is to use a wort pump and a heating element, and pump warm water through axial channels in the chamber. This is obviously a bit bulky, but given that the chamber alone will mass around 25kg, I presume it's not intended for long hiking trips. The propane tank could either be war...

I don't have any links offhand, but I did build one back in '07, before I joined Spudfiles. The maximum combustion pressure in such a mix can be about 23atm, as opposed to about 8atm for an air/propane mix. This occurs around 3:7 oxy/propane, as predicted by GasEQ (which you really should be using, ...

...i found a paper mentioning the use of a tapered sabot catcher which use the deformation of the sabot to augment the speed of the gun... I found it too. The trouble I'm having is actually measuring the speed to start with :P The fuel mix is rich enough that the exhaust gas becomes a 2m diameter f...

Your pre- machine tools ETG certainly works better than mine did! The craters have different aspect ratios because you were using heavier BBs, but I'd say this works just as well as my last pure ET gun did (before I introduced the aluminum fuel). I also suspect that the finer grade of aluminum powde...

Hey Equus. It's good to see someone else involved in the high speed side of things. I'd be interested in seeing the gun used to make the crater in your profile picture, especially given my soft spot for ETGs. My crazy projects continue apace, but they don't fall within the scope of this forum at the...

burning_water wrote:Thanks DYI,
I am glad you like it.
What sort of pressures have you been using on your setup ?

Between 1000 and 2000psi fuel pressure with a 0.85:0.15 hydrogen/oxygen mix.

Nice photo of the muzzle blast. And good production rate on the electrolysis rig, that's impressively cheap, even if you have to replace the plates with 316 yourself. I've considered doing this a few times, but I ended up taking the route of just renting oxygen and hydrogen tanks, mostly because my ...

If you can produce an adjustable gap, and set its width with a shim of known thickness, you can use nearly any HV source for hybrid ignition. Including piezoelectric barbecue starters. With a spark gap width of 0.003", I can ignite a mix at 1700psi starting pressure using an electric barbecue starte...

Good to know i should be able to use standard firearm twist rates. I wasn't sure if the lower forces involved with air would change things dramatically. Various factors will change things dramatically here. Most important is the relation between the projectile mass and its diameter - for plastic sl...

i have no idea what range i can expect from such a rig, or where to look to find out. Use GGDT (freely available, easy to use) to predict performance and range to decide on the launcher's parameters, if you decide to go with a pneumatic. As I mentioned soon after you asked the question initially, G...

The air motor sounds like a much better idea, assuming you have a compressor that can keep up. The performance curve is definitely in the right range, although I'm unable to find the LZB 44 in the current catalog. Are you sure it's not actually the 42 or the 46?

Pump is 2cc/rev, maximum 230atm, motor output is probably about 210W after losses. Pressure work at constant pressure is P∆V. So, the work done in a single pump revolution at 230 bar is 230*100 000*0.0000022=51J. This would imply that you could get 4 rev/s or 240rpm if the motor was geared such that...

Do you include heat loss? Seems to me like that would be the hardest part. High velocity flow of 2500C gas through a 30C barrel would, I would SWAG, have pretty significant heat loss. Or, is the heat loss low enough in the time frame of a firing gun that it can be neglected? In a typical closed cha...

Nice work. What is GALE? GALE is actually a quasi-1D Lagrangian CFD code I wrote last summer. I've never heard of that thing jrrdw posted before. It was designed with the ability to quickly predict the performance of gas guns in mind, including multi-stage guns. It currently does not support chemic...

What are the restrictions on attaching things to the bottle to make it more stable in flight? Or is that against the spirit of the contest? :lol: Regardless, the best way to go about this is probably going to be a low mix hybrid, oxy/fuel combustion, or burst disk pneumatic, depending on how much ba...