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Spud gun. Help me please

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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Spud gun. Help me please

Unread postAuthor: beastmode986 » Thu Apr 05, 2012 4:23 pm

Ok I recently made a spud gun.just a casual one it has a 3" chamber and 2 inch barrel the barrel is about 3 ft long maybe a little longer. 4 ft max and the chamber is like 2 ft long with a 3in to 2 in adapter I'm using a regular grill igniter for my ignition system. I'm having 3 problems .
1. I get a lot of misfires , I use hairspray for a propellant
I'm not sure what the problem is. Any suggestions on what a Better fuel would be . Should I make a propane meter and use propane?
2. On a lot of my air cannons I get leaks I'm not sure why because I always use job weld or Teflon tape. But on this spud gun I jb welded the igniter in and sometimes it leaks out hot air from the job weld how can I fix this? Just add more?
3.the cannon isn't very powerful it doesn't shoot very hard , I was shooting a piece of PVC pipe wrapped in electrical tape with the front sealed and it shot like 35 ft and it wouldent do any damage

What should I do to fix these problems? How can I make the cannon better? Thanks in advance.
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Unread postAuthor: natas » Fri Apr 06, 2012 4:05 am

sounds like u use too much hairspray.

what brand u should use depends a little on where u live in the world. and what u have avaiable.

a meetered system will always give u more accurate and controlled explotion.(read more powefull)

there is a few treads here talking about different spray and pray propellants
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Unread postAuthor: natas » Fri Apr 06, 2012 4:19 am

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Unread postAuthor: DEATHSTAR » Fri Apr 06, 2012 8:27 am

If you're using "Hairspray" and getting results,
Probably that brand uses propane for the "propellant" gas.
The rest is sticky residue that just makes a mess.

A "spray and pray" is always just that...You spray some (propellant or gasoline drops) in and "pray" it will fire.
SO YES, use propane and a metering pipe.

I've found it easiest to use "Metric" measurement, and calculate about 5% volume of propane GAS at atmospheric pressure.
For small chambers: I go to CVS or whatever pharmacy and ask for a "Baby oral syringe" I don't use it for the meter pipe, just for determining meter volume/chamber volume (using water usually).

To get propane in gas volume, I need the tiny pin-hole propane torch tips.
There used to be a link (store on here) that sold smaller one's but I don't see it (or know where to get one???).

Be carefull because in a lot of states, Anything which uses an "explosion" to project the [whatever] iS considered a "Firearm" depite Federal Law.
Good luck! 8)
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Unread postAuthor: jsefcik » Fri Apr 06, 2012 11:38 am

starting fluid works awesome!!!

with chamber fan
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Unread postAuthor: jimmy101 » Fri Apr 06, 2012 6:03 pm

4% (by volume) for propane in air at 1X. (Not 5%)

Search the spud wiki for "syringe" and start with a syringe based meter. It'll cost a tiny fraction of what a pipe based meter costs. (A syringe meter can be done for less than $5, including the fuel source.)

Next thing is a chamber fan. You can get about the same performance without the fan but you need to wait two or three minutes after fueling to let the gases fully mix.

A syringe plus patience will get basically 100% of the possible performance out of the gun. A dedicated meter, fan etc. make the gun slicker but won't improve performance.

You shouldn't have epoxied the sparker into the chamber. Use a pair of fine thread deck screws as the electrodes and connect them to the sparker with wire. (Deck screws have sharp points.) The screws won't leak.

I sure hope you used the proper glue. If the gun is PVC it should have been assembled with PVC and nothing else.
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