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New gun, need sugestions

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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New gun, need sugestions

Unread postAuthor: sea donkey » Mon Jun 11, 2007 8:30 pm

This is my first attempt at building a spud gun. I have 4" x 15" chamber, a 2" x 5' barrel, and a grill igniter. I'm not sure how long to cut my barrel(C:B ratio I think), or how much fuel to put in. I've tried bug spray and starting fluid, and only got it to shoot once with bug spray. I tried all diff. amounts of starting fluid and still no shot. Please help.
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Unread postAuthor: NoXi » Mon Jun 11, 2007 8:43 pm

how long do u spray it in for?
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Unread postAuthor: spudthug » Mon Jun 11, 2007 9:20 pm

did u mount the ignitor right into the gun? if you did thats a very bad idea...its allways very very picky and the gap it probably really small...

put two screws into the gun and hook wires to the ignitor then hook the wires to the screws..
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4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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Unread postAuthor: noname » Mon Jun 11, 2007 9:23 pm

Sometimes starting flud isn't vapory enough to ignite, and never use bug spray. Most bug spray has a bunch of icky solvents in it that dissolve the solvent welds in pipe, which isn't good.
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Unread postAuthor: sea donkey » Tue Jun 12, 2007 6:37 am

Thanks for the input. I tried all different spray times. I did put the grill ignitor in the chamber. I'll try putting screws in.

How far apart should I put the screws?

What would a good fuel be?
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Unread postAuthor: NoXi » Tue Jun 12, 2007 4:49 pm

the fuse should be around a 1 cm apart. Hairspray, axe, stuff like that are good fuel
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Unread postAuthor: paaiyan » Tue Jun 12, 2007 6:54 pm

I use static guard in my spray & pray. Works like a charm, I get around 200 yards on a good day. Of course my cannon is over 8 1/2 feet long, but you should be able to get good results.
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Unread postAuthor: Bubba05 » Wed Jun 13, 2007 10:15 pm

Even carby start is good fuel!!

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Unread postAuthor: Scotty » Thu Jun 14, 2007 10:10 pm

If you use Propane as fuel the percentage sholud be 4-7% of the total volume of your chamber ( If your chamber is 1000ml you need to use 40-70cc of fuel) Your c:b ratio should be around 1-0.7 (Chamber 1000ml Barrel 700ml) To find your volume the formula is 3.1416xRadius squaredxlength of chamber ie. 3.1416x2580.64x381=3088ml .
You would need to use a barrel with a capacity of approx 2161ml or approx 3 feet long if you use the 2inch stuff ( you should cut your chamber in half is my humble opinion) that way you only need 1 1/2 feet of barrel. You will need to use around 150cc of fuel the way the chamber is now.
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