SpudFiles

As per title, does anyone have any solid data on such an oxygen+fuel mixture in small launchers? All the search feature seems to turn up is warnings not to do it

edit: In a nutshell (or should that be brass ), the idea is to have such a system in a small 6mm cartridge like so:



...which would be fired from a semi-automatic action with a piezo ignitor, like so:



Worthwhile power, what does the board think?

Well asides from the obvious (you get a 5x as aggressive combustion) you are opening yourself up to DDT due to increased flame front speeds but it's still unlikely.

Larda did use oxy-propane in 40x mixes (equiv to 200x) so it is do-able, but I think he noted it wielded poorer shots.

You also have the issue of the oxy-nitrogen mix already present in the chamber, meaning you have to compensate for that or try to purge the chamber.

I can add more info is you elaborate on what fuel you would be considering.

I'm not thinking massive quantities, say a 5x mix in a cartridge similar to the one illustrated for a 6mm projectile.

Both oxygen and butane - the fuel I intend to use - are heavier than air so I'm guess it could be fuelled with a syringe.

With those dimensions by my calculations I would need to add roughly 0.4cm³ of butane and 1.4cm³ of oxygen.

Sorry if I'm being stupid, but how do you pressurize that exactly? Or will it have some kind of valve added..

If you can, go propane. It's so much more reliable..

inonickname wrote:Sorry if I'm being stupid, but how do you pressurize that exactly?

That's the whole point of using oxygen, it's not pressurised at all.

jackssmirkingrevenge wrote:

inonickname wrote:Sorry if I'm being stupid, but how do you pressurize that exactly?

That's the whole point of using oxygen, it's not pressurised at all.

Ohhh...far out I'm thick. Should have realized that pre-purging with O2 would let you use a mix very close to 5x. In that case, it should be easy.

The idea is to be able to make a small calibre shell-ejecting launcher with "realistically" sized brass cartridges that can fire semi-automatically, with enough power to eject a spent cartridge (by means of an angled bolt tube as I did here and drive the bolt far enough to chamber another cartridge.

It should also have worthwhile power, I'd be happy with 400-500 fps for a 1 gram projectile.

This is what I imagine the launcher to look like in basic functioning terms:

If you were very enthusiastic you could use a flyback generator or a marx made with pulse caps for full automatic. Sure, it would give you limited portability and have the slight risk of killing you if you happen to touch the contacts, but full automatic hybrid ejecting shells would be too cool..

Jack, I know you're keen on using the same material for both cartridges and barrel but wouldn't it be more efficient to use short fat cartridges (although harder to make) rather than longer thin ones?

First of all, you'd need less travel in your system to eject and reload, and secondly thinking that the cartidge is likely to be moving back as the projectile is moving forwards, then a short fat cartridge would mean less pressure is needed to propel it backwards. It's a bit like the stepped piston idea in gas repeaters.

inonickname wrote:full automatic hybrid ejecting shells would be too cool..

Too cool and too time consuming to load the cartridges, I'd be happy with semi-auto. It gives you time to appreciate the individual clatter as each cart hits the ground

I know you're keen on using the same material for both cartridges and barrel but wouldn't it be more efficient to use short fat cartridges (although harder to make) rather than longer thin ones?

That's the point really - using the barrel material completely eliminates any alignment issues , and makes manufacture much more straightforward.

I agree though that using a fatter cartridge gives you a lot more mechanical advantage when it comes to shell ejection, I found this out while testing my preloaded cartridge prototype (and you pointed it out there as well )

JSR wrote:The main reason I abandoned this design was the lack of power blowing back the cartridge, mostly because the massive (in comparison to the 6mm valve port) 0.75" barrel that didn't allow sufficient pressure buildup. I was aware of this point but SPG brought it up recently and got me thinking again.

I did a small experiment and blocked off the breech with a 6mm aperture to see if it would make a difference. To say that it worked is a bit of an understatement, even without a projectile the thing blew back with such violence into my hand that it turned the tip of my finger purple

Well I like to be consistant you know.

Couldn't you sleeve both cartridges and barrel? I'm trying to remember whether I've seen any thick walled tubing with a 7mm ID, but that'd be idea surely? Then you wouldn't have any alignment worried cos you're still using the same materials for both barrel and cartridge.

JSR,

An easy way to figure if this is plausible is to look at how much energy you have stored in the cartridge. I figure those dimensions (6mm or .22 by 2.5")
will have about .1 ci in each shell.
I believe oxy-butane would give a little less than 20,000 joules per liter, so you have about 30 joules to work with. 20% efficiency would give you 360 fps with a 1 gram projectile.


Pressurized carts are easy to do though;
2 copper endcaps with holes drilled in them, one gets a schrader stuck in it, the other gets a thin steel burst disk soldered over the hole. Both are soldered onto a length of copper tubing.

The rubber on the schrader will insulate a path for your spark to travel through.

_Fnord wrote:Pressurized carts are easy to do though;
2 copper endcaps with holes drilled in them, one gets a schrader stuck in it, the other gets a thin steel burst disk soldered over the hole. Both are soldered onto a length of copper tubing.

It is easier for a rich man to pass through the eye of a needle, than it is for a camel t....than it is, for a camel to. That's still too complex (and heavy) compared to what I'm after.

The performance figures are a bit marginal, maybe a short fat cartridge is inevitable. Let's see, 0.5" I/D an inch long will give me double the volume...

the shell would have to be slightly pinched to keep the bb from coming out.
why don't you use a primer for a black powder rifle i don't know if it is against forum rules to use primers to set off a charge but then you would only have to smack the primer to set off your charge and that would open you cannon up to full auto capabilities

spudtyrrant wrote:the shell would have to be slightly pinched to keep the bb from coming out.

Easily held with some tissue wadding or a drop of wax.

why don't you use a primer for a black powder rifle i don't know if it is against forum rules to use primers to set off a charge but then you would only have to smack the primer to set off your charge and that would open you cannon up to full auto capabilities

Even with a primer alone it will give performance equal to high-end air rifles, but aside from the forum rules there is the issue of supply as well as a considerable amount of force needed to smack the primer for ignition, which makes the cartridge reloading more difficult.