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Shooting Marbles ???

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Shooting Marbles ???

Unread postAuthor: Rob748 » Sun Mar 01, 2009 2:32 pm

Im in the process of building a Advanced Combustion Cannon that will shoot marbles that are around .65 in diameter. The Combustion Chamber is 15 inches long by 3 inches in dimater. The Barrel is 60 inches long by .75 in diameter giving me a 1:1 ratio . It will have a 2.5 inch computer fan inside, that will run off 12 volts. Im still building the meter for the mapp gas. Ill have cam couplings so I can split the barrel and put a burst disk in. ( what kind of material will hold to 45 psi ?) A guy ran the specs into a Hgdt program and it said it would shoot in the 1100 fps with a burst disk that held to 45 psi. Im not expecting that much fps, I'm hoping for around 850fps+. Heres my main question, if the projectile, a marble for example isnt the exact size of the barrel, how would you get a good seal ? Or do you have to find the right size barrel ? What size of Barrel is required to shoot marbles, I know marbles come in a few sizes?.

Thanks, I just need some ball valves and Ill have some pics pretty soon :D
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Unread postAuthor: mark.f » Sun Mar 01, 2009 3:09 pm

Normal glass marbles that you would find in the hobby section at Wal-Mart fit near perfectly in 1/2" type M copper tubing. A few to the majority of them actually won't fit, depending on the lot you're buying from, because the fit is so close.
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Unread postAuthor: john bunsenburner » Sun Mar 01, 2009 3:18 pm

Well, persuming you mean the barrel is too big for oyur projectile i am pretty sure you can't get a good fit with a barrel that is too big(really?). I soem how(totally) doubt you will get any where near the velocity you are expecting with 45psi. I suggest downloading HGDT your self and finding out. So to sum things up:

1. Find a barrel with a good fit
2.Get HGDT and find out if your figures are correct.

The only other alternative to get a good fit would be to sabbot the marbles or to wrapt them in duck tape until they do fit.
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Unread postAuthor: CpTn_lAw » Sun Mar 01, 2009 3:30 pm

Hi,
850 fps is pushing it a little with a combustion, look at Chaos' pneumatic gun, he pressurized it to 400 psi and managed to get a marble to 900 fps . I'd say 400 if you're lucky. A .65 marble weighs just over 5 grams on average.
To get a tight fit, there are two main options I can think of : first a sabot of the exact (or close enough) diameter of the barrel. Second : some sort of wadding...
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Unread postAuthor: Rob748 » Sun Mar 01, 2009 4:14 pm

Lol I wish I could download hgdt
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