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First spud gun - Will it work??

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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First spud gun - Will it work??

Unread postAuthor: Jimmy » Sun May 25, 2008 3:56 pm

This is my first spud gun and before i build it i want to know if it looks alright.
I will be using a 100k stun gun for ignition and a brush less fan for mixing and cleaning.

1. Should i use more than 1 spark..inside the chamber

2. Is the barrel and chamber a good length

*see picture below
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Unread postAuthor: SpudFarm » Sun May 25, 2008 4:04 pm

looks good there:)

you can just install 2 gaps in the chamber. better ignition is allways a pluss.

and you could need a longer barrel.
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Unread postAuthor: Spuddin » Sun May 25, 2008 4:10 pm

i'm no calculator guru so i just build'em as i feel is right and i would have to say the chamber is too long for a combustion, i would shorten the chamber for sure if your wanting to stay with the 4 foot barrel. my guestimate would be a 2 foot chamber maybe shorter but someone with more knowledge will post the correct length soon.
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Unread postAuthor: starman » Sun May 25, 2008 4:22 pm

Your chamber is unnecessarily large. Cut it in half and add a foot or so to the barrel. I haven't bother to calculate the c:b volume ratio of this (too lazy at the moment) and it still won't be ideal but it will be better optimized than the plan you have drawn up, and still be practical for portability.

For your c:b volume calculations, the elbow system should also be calculated in the chamber space.

Also, instead of a clean-out cap on the end of chamber, put a 1" or so PVC ball valve there...easy open fresh air intake...assuming you're going with a meter propane of course.
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Unread postAuthor: Jimmy » Sun May 25, 2008 5:16 pm

Thank you...I will definitely take all of those ideas into consideration.
As this being my first Spud Gun i am not going to use propane but may upgrade it to that in the future.
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Unread postAuthor: Boom_erang » Sun May 25, 2008 5:51 pm

A chamber of 18" will give you a 1.5:1 ratio (I have that on my 1.5" gun) and it should work well. Many tests point to a .8:1 ratio as being ideal, so you may wish to reduce your chamber further. I'd say anywhere between 1 ft. and 18" should give you good results without a huge muzzle flash or super-loud "bang".

I like the over-under approach but haven't built one myself yet. Yours will probably work great - let's see some pics/vids when done!

-B
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Unread postAuthor: Jimmy » Sun May 25, 2008 10:50 pm

I will definitely put some pics and videos on the site. Thank you for the advice I will make the chamber much smaller - in the 1ft to 18in range -
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