SpudFiles

my idea is a combustion cannon that would work very well as a semi auto and possibally a fully auto.
the idea comes from the internal spining bolt that i have seen on another thread and basicall involves a regular combustion set up but the spinning bold in the barrel close to the chamber, the idea is that you have the bolt spin to let ammo in then as the cannon fires a small gas pipe from halfway up that barrel pushes a small piston on a spring return that is connected to a cam that turns the bolt only half a full turn then the spring returns the piston back to its normal closed postion due to pressure from the combustion no disipated.
that part is simple
now the other side of things is the chamber and refueling side of things, this can be done with propain at high pressure connected to a nitrous oxide purge valve, this will allow quick refueling as quantity could be worked out by how long the valve is oppened for.
once the cannon has fired i think a quick burst of CO2 could clear the camber and refuling could take place.
another thing is that as im writing this up i thought if you used an ignion coil from a bike ( only needa a small 9v battery) could supply the spark thats connected some how to the cam on the spining bolt to provide the break in the ciruit and would spark as long as your finger is on the button if your in fully auto mode or as and when you need if your in semi auto, a cocking handle could provide the inital turn of the cam or if there is a stopage.
( sorry for the detail, i used to do alot of rifle shooting)
but anyways theres my idea, please pick it to peices and give opions

c02 is inert so you could not purge with it

sorry im a bit simple what do you mean inert?

CO2 doesn't burn, so you're going to have to purge with something else.

Have a look at how a combustion nailgun works (scroll odwn to find it) for some inspiration

no no no i ment just to 'flush' the exhaust out of the chamber before the other tank of propain of what ever is then injected
its kind of a forced clear out

What is the use of flushing the chamber with CO2?
What you need is to get fresh new air and thus oxygen.

The CO2 does push away the burned air and fuel (which is basically CO2 and H2O) but then you still got a chamber full of CO2.

Its like flushing your toilet with pee.

You need to get AIR into that chamber, not CO2.

very gud point, right scrap C02
O2 is the way
thx


'trying to flush your toilet with pee'
i gotta remember that one for work

Ehmm, are you going to use pure O2 now?
I think I should give you the following information so you dont kill yourself:

When the oxygen concentration is higher then normal (20%) burn speed increases significantly and DDT is there before you know it.
Also the extra amount of oxygen allows you to inject more fuel which basically makes your guns performance like that of hybrids.

Never, ever use oxygen enriched mixtures in PVC cannons.
The shockwaves and pressures generated WILL blow up your chamber and put the sharp remainings of it into your body at high speed.

i think there is some confusion here
ok yea i didnt think about how i worded that but all i want to do is vent the camber ready for the propain/butain fueling,
so from what your saying, i cud just have a tank of just normal air you breath and presurise it, when the bolt is open i force air through the chamber out into the atmospere thus ready for the refueling stage
i dont intend on turn hybrid on this so i wont pressuise the chamber so to speak

use a fan

a fan whould take too long i want a sudden and fast rush of air to vent the chamber,
im going for as fast reloading as i can here lol

Use compressed air.....

that is what i have come to the conclusion
but what about the actual theory if the thing? can anyone see a reason why it wouldn't work?

The "theory" says it will work. The practical aspects are what'll be a PITA.

Semi-auto shouldn't be huge problem. There are a few tricky parts besides the mechanism. One is that the second and subsequent shots start with different gases in the chamber than does the first shot. The first shot has clean air (~79%N2, 21%O2). Subsequent shots have no O2 left in the chamber. To purge with fresh air you'll need to flush the chamber with at least a couple chamber volumes of fresh air. That takes a while unless you can open up a pretty big vent valve and use a high pressure high volume air source. "Takes a while" means that doing it in a second or less is going to be very difficult.

Full auto is easy once semi works but the ROF will suck. You just can't flush the chamber out fast enough for full auto to be any faster than semi. Even the low ROF of a real machine gun (~300 rounds/minute) means you would have to purge and refill the chamber in about 0.2 seconds. I can't see that happening. You might be able to do it in a couple seconds but that would give a ROF of something like 20 rounds/minute. That's basically semi-auto type fire rates, the fact that you don't have to release the trigger makes if "full-auto" but the ROF is no better than the semi-auto.

The other big problem is that even after you flush the chamber, then inject the fuel, you have to mix the fuel. That takes a while even with a good fan. "A while" means a couple seconds or so. The fan mixing time alone will limit the ROF to a few tens of shots/minute.

If you are really serious about this, and your careful, the best way to go is to skip the venting step. Fire the gun then inject the proper amount of pure O2 (20% of the chamber volume) then the proper amount of propane (4%). Mix with fan while the ammo is being chambered, fire, repeat.

There is another possibility but it is extremely dangerous. If you have a pressurized bottle of premixed air+propane then the purge/fuel cycle is a single step and you don't need the mixing cycle. The HUGE danger is that the premix is flammable. Get a flame propagating back into the premix resevoir, such as might happen if a valve doesn't close fully, and your premix chamber is gong to explode. Like I said, not a good design.

the other option is to have rotating chambers that take turns filling, firing, and venting, like a Gatling gun, only with the chambers rotating rather than the barrels. This way you could cut the effective cycling time to a half, third, or 100th, depending on your system. It a certain point it makes more sense to have a barrel for each chamber, that rotates with it. Something like this was done, as I remember, lemi search it up for you.

http://www.spudfiles.com/forums/revolver-x-t174.html

well it turns out it isn't nearly as good as I remembered it. You could do much better incorporating a similar auto system with multiple chambers and barrels.