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20 Cubic foot oxy bottle cannon idea

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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20 Cubic foot oxy bottle cannon idea

Unread postAuthor: steven_main » Tue Oct 30, 2012 12:29 pm

bottle is Stamped DOT-3AA-2015 (pressure tested safe work rating)
Just want to be certain this idea sounds safe and effective to the experts for 10X burst disk hybrid.

Basically remove the valve from the tank and install a Schedule 80 Pipe Adapter to 2" shedule 40 theaded barrel. In this adapter I will drill and tap two locations with 1/8NPT thread.. one for the ignition module, and the other for charging and fueling. In reality I will only fire 7X via remote control and 4X shoulder fire.
HGDT predicts 4,200 ft lbs of muzzle energy at 4x and 500PSI pressures...
Remote fired at 7X it would achieve 6,500 ft lbs and 913 chamber pressures.

Will such a design prove effective? also is it safe for shoulder fire?
What happens if get a DDT? I cant imagine how I could build this to be any more safe.
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Unread postAuthor: sagthegreat » Tue Oct 30, 2012 12:40 pm

I wouldn't trust that thing on my shoulder, it ways a lot plus all the recoil. I mean its double the energy of a .50 BMG.


I would make it to mount on my car something lol
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Unread postAuthor: steven_main » Tue Oct 30, 2012 12:50 pm

Actually Ive looked at some ballistics charts .50 BMG was listed as 12,700 ft/lbs So Im only half that. Ive fired thousands of rounds out of an M2 .50 cal machine gun and although I cant say Ive shoulder fired one lmao... and it has a recoil system, and it can make a 9,000 lb armored HMMMWV rock back and fourth I would think something 1/3 the power could be safely shoulder fired. Im guessing the system would weigh about 50lbs so not too horrific.
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Unread postAuthor: MrCrowley » Tue Oct 30, 2012 1:03 pm

I think shoulder firing at 4x should be ok, as long as you have a good grip on the gun there's no reason it can't be handled.

The problem with the oxygen tank is its small opening, how do you plan on mitigating that? Not sure if you covered that when talking about the sch80 adapter but you'll want to drill a bigger porting in to the tank and weld some threads in. I would say a 1.5" - 2 " porting would be good. If you don't enlarge the porting, you're just wasting an oxy tank.

DDT shouldn't be a problem either.
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Unread postAuthor: steven_main » Tue Oct 30, 2012 1:08 pm

The opening is about 1" diameter is that really too small?


Ill be getting a Tig Welder soon, if I do cut and weld Its not going to be a cheesy flux cored mig weld I just dont want to compromise the pressure vessel

another problem Im finding is the "black steel" fittings im finding are only rated to 150 PSI!? thats worse than PVC somehow?!
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Last edited by steven_main on Tue Oct 30, 2012 1:16 pm, edited 1 time in total.

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Unread postAuthor: MrCrowley » Tue Oct 30, 2012 1:13 pm

Well it's a bit of a waste. Unless you're using a 10' 1" barrel, you may as well use something else for the chamber.

I can put a golf ball barrel on a 3/4" union hybrid and get decent results but increasing the chamber size doesn't make much difference unless you start increasing the barrel length as well.

If you want a cannon for firing projectiles 1.5" or above, I'd go with something that has a bigger opening.

edit: a 10' or so 1.5" barrel would probably work too. However, seeing as you want 4,500ft/lbs from a 4x mix, I assume you're using a larger diameter barrel.
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Unread postAuthor: steven_main » Tue Oct 30, 2012 1:22 pm

Ive seen your vids on you tube... big fan. Anyway a 1.5" barel would be ok too, plus would reduce the packaging weight. and by a 20 cubic foot I want to make sure everyone unfamiliar with welding knows its only a 5" x 14" bottle weighing 15 lbs with 274 cubic inches... 20 cubic foot is compressed oxy volume.
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 30, 2012 4:10 pm

Assuming your fittings are all up to it, should be a much safer project than your last effort :)

As to barrel size, MrC makes a good point - remember that a 2" hole allows 4 times the flow as a 1" hole. Still, in spite of this it would still be bloody impressive with a 2 inch barrel. Also, it would seem a pity to waste such a large chamber on a small bore, but on the other hand you would get great performance without having to use higher mixes.

steven_main wrote:and by a 20 cubic foot I want to make sure everyone unfamiliar with welding knows its only a 5" x 14" bottle weighing 15 lbs with 274 cubic inches... 20 cubic foot is compressed oxy volume.


It's roughly three litres if I remember well.

The question is, what do you intend to fire out of it? A bigger bore gives you more options, but then making sabots becomes more difficult.

Find out which size of soup tin you have wide access to and choose accordingly, the world is then your oyster :)
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Unread postAuthor: sagthegreat » Tue Oct 30, 2012 5:20 pm

get a spring system on your shoulder stock, and you should be okay lol
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Unread postAuthor: steven_main » Tue Oct 30, 2012 7:48 pm

Hell I was just gonna hold on for dear life but maybe some pistol grip and a padded shoulder stock is in order.

Maybe a trunk gas strut on a hinged shoulder pad with a tab on the barrel
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 31, 2012 12:43 am

Recoil will be substantial but won't knock you off your feet.

This is probably what awaits you:

[youtube]http://www.youtube.com/watch?v=PAt0ILc5GOI[/youtube]

Of course if the line of thrust is over the shoulder it's going to be more difficult to hold on to than if it was actually a straight line into your shoulder like a conventional rifle.
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