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A place to ask general spud cannon related questions.
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Unread postAuthor: starman » Sun Feb 15, 2009 9:45 pm

If you haven't already, go get HGDT. You can model your gun to your heart's content.

If you must keep the chamber. Don't go over a 2x mix. Go for a 4" dia., 10' long steel barrel. Not sure what the heck you're going to do for a burst disk holder and burst disk material. Find a 4" burst disk that will burst at somewhere between 100-200 psi....good luck on that.

Here's what you can expect:

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Over 20,000 ft*lbs of energy and 575 ft/sec velocity...yeah that ought to take a small tree down if hit right.

Don't worry, it will be loud.
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Unread postAuthor: daberno123 » Sun Feb 15, 2009 10:02 pm

My idea for a burst disk holding would be some sort of homemade flange. Weld two steels plates, one on the chamber and one on the barrel, put a gasket in between, and then bolt them together. It would be way cheaper than buying a 3" or 4" union to weld on.

Of course reload time will increase, but really when you build on on this sort of scale some things end of being sacrificed for others, mainly ease of use for more power.

Look at FEAR, IIRC Killjoy used some sort homemade flange to hold his burst disk in place.

In regards to the actual burst disk, thin sheet metal is probably going to be your best bet. IIRC D_Hall is using 1/4" steel plate on his monster to burst at 100 psi.

One more question. Do you have a suitable area in which you can actually fire this safely? You're NOT going to want to shoot within a few miles of habitation and without at least a mile or two of wilderness downrange.
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Unread postAuthor: brogdenlaxmiddie » Sun Feb 15, 2009 10:09 pm

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Unread postAuthor: D_Hall » Sun Feb 15, 2009 10:57 pm

brogdenlaxmiddie wrote:Whats the biggest hybrid in terms of chamber size?

Suffice to say I've got 30' of 30" pipe invested.

(Gun is far from finished, however, so you may say that nothing counts until a projectile is fired.)
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Unread postAuthor: brogdenlaxmiddie » Sun Feb 15, 2009 11:29 pm

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Unread postAuthor: starman » Sun Feb 15, 2009 11:44 pm

FEAR is the largest one I can recall without an extensive search.
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Unread postAuthor: Fnord » Mon Feb 16, 2009 11:17 am

I see everyone is putting their recommendations up, so here is mine.

_____________
Chamber stuff:

As D_hall suggested, I would also recommend at least 1" thick end plates. Maybe you should ask your buddy if he has any way to get rounded plates though?

I wouldn't limit myself to 2x, but I wouldn't be standing next to it either.
And I wouldn't be too concerned with DDT. You should be using more than one spark gap anyway.

I did a calc on hgdt, and the difference between a 72" chamber and a 48" one was only like 3500 ft-lbs @ 5x. Your call though.

I can't really recommend over 3" porting for a 4" barrel. You'll see a 5-10% performance loss, but a 4" disk would probably be more trouble than its worth.

_____________

Barrel stuff:

Steel thinwall conduit is probably the way to go. 10' of 4" will probably weigh around 70 pounds, but it's infinitely cheaper than aluminum.
Plus 4" is actually 4.33" ID, which gives a noticeable power boost.

If you buy it new, expect to pay up to $100.
Mcmaster has 3 & 4" conduit for 60 and $80 respectively, but shipping would kill you.
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Reasonably optimal figures.

I should also point out that you could get around 100,000 ftlbs with a 20' barrel. I wouldn't cut the chamber down any if you plan on this.
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Unread postAuthor: psycix » Mon Feb 16, 2009 12:18 pm

brogdenlaxmiddie wrote:I'm sorry to say that the pipe dream doesn't count. :roll:

Nope it doesnt count unless you post a vid and damage pics! :roll:
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Unread postAuthor: cdheller » Mon Feb 16, 2009 7:01 pm

Soo any chance of getting more info on this pipe

"10" " steel pipe varys from .134 to 1.125 in wall thickness ,is probably biggest factor on its pressure rating but alloy and seamed or not play a part also.
If you goggel you can find the formulas or charts to work out other parts
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Unread postAuthor: brogdenlaxmiddie » Mon Feb 16, 2009 7:04 pm

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Unread postAuthor: jonnyboy » Mon Feb 16, 2009 8:13 pm

brogdenlaxmiddie wrote: For the endcaps, does it really need to be an inch thick? Can it be something more realistic like 3/8 or 1/2??

I certainly wouldn't want a blow out. :shock:
If you can get less thick plates cheaper you could just combine them...but that might not be the case.
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mobile chernobyl wrote:I can shoot a Canuter Valve off my '82 Chevy Ram F150 AT LEAST 3/4 Mile with 'ma cannon made of soup cans duct taped together, then I just squirt some bacardi 151 in the chamber and hold up my cigarrete lighta and WHOOSH! That thing flies at least 3/4 mile
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Unread postAuthor: D_Hall » Mon Feb 16, 2009 10:41 pm

brogdenlaxmiddie wrote: But I do have a question. For the endcaps, does it really need to be an inch thick? Can it be something more realistic like 3/8 or 1/2??

As long as you're talking flat plates... Yes, it really does need to be thick. Flat plates do NOT support such loads well at all.

Want to keep it to a reasonable thickness? Get a bullnose (ie, "giant end cap"). I just purchased one for 30" pipe that cost on the order of $800. By that measure, a 10" bullnose will probably cost on the order of $250 (just a WAG, mind you).
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Unread postAuthor: Fnord » Tue Feb 17, 2009 8:55 am

But I do have a question. For the endcaps, does it really need to be an inch thick? Can it be something more realistic like 3/8 or 1/2??


You could also try to find some type of pressure vessel with rounded ends and cut it up. I have a hydraulic cylinder that just happens to be about 10" in diameter, but I don't think I could give it away.
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Unread postAuthor: starman » Tue Feb 17, 2009 10:33 am

_Fnord wrote:You could also try to find some type of pressure vessel with rounded ends and cut it up. I have a hydraulic cylinder that just happens to be about 10" in diameter, but I don't think I could give it away.


I thought the same thing ... However, he seems determined to used the oversized pipe in his backyard.
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Unread postAuthor: Fnord » Tue Feb 17, 2009 10:49 am

I thought the same thing ... However, he seems determined to used the oversized pipe in his backyard.



I know. What I was thinking of is cutting the ends off a similar diameter vessel and welding them on to the pipe. Once we actually get some rough measurements it'll be easier to tell whether this is going to be a realistic project.

However, a big oxygen cylinder would indeed work great and be very safe for this project.
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