waxman
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dimethyl ether
Looking for non-sticky alternatives to hairspray as a fuel for a spudgun. Any ideas?
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Swany
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Build one of these: http://www.apcforum.net/files/DSCN4725.jpg
That would be my direct propane injection system. With a known volume of the expansion chamber, and the combustion chamber, you can calculate the
stoich. amount of propane to inject via reading the PSI (50, in my case), and you get a perfect shot every time. 4% in air is about stoich.
EDIT: Also, a cylinder of propane basically lasts forever. I am not going to calculate the amount of shots, but... well... in retrospect, I know
everything I need to...
[Edited on 30-4-2006 by Swany]
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waxman
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Thank you, Swany! I've built a propane injector, but using a 6" X 1/2" pipe section as a "resevoir". My combustion chamber is 3" PVC X 24" long. Tried
different pressures, 30-60 psi, but if you're saying 4%, I've been waaay too rich! (No fire) Will try leaning it down a bunch! 
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neutrino
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You could always try starting fluid from your local auto parts store. It's basically diethyl ether and short-chained alkanes (C6-C7, usually).
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Swany
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Yeah, the most common mistake is to overfuel. Propane is flammable in air, with a good spark, at percenteges roughly 2-9%. Mind you, at these
percentiles, you will be firing at about 20-30% the power of your optimal mixture. At optimal mix, you should see a blue tounge of flame shoot about
1ft out of your barrel, at night. You can also dry-fire it without a projectile and it will still 'boom', if your mix is right.
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waxman
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Indeed! Cranked the propane down, and boom! Nice! I'm shooting the gas in by an air chuck/Shrader fitting so I can use the fuel supply amongst a few
guns!
Starting fluid? Hmmm. Back to the range........! 
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markgollum
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I have a spud gun and in my experience methyl acetylene (MAPP gas) and misted methanol work the best. However I have not tried ether or acetylene as
the acetylene would probably destroy my gun and I haven’t gotten around to making ether.
I have not been impressed with the performance of propane in my gun, it is difficult to manually add the right amount and even when everything is done
right, propane never has the “UMPh” of methanol, never mind MAPP gas.
MAPP gas is my favourite because it is very powerful and has a large margin for error (as far as adding to much/little).
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Swany
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http://burntlatke.com/lpmapprussets.html
Some figures regarding MAPP and propane gasses.
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markgollum
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Wow, that is a great link, I would never have expected the power of propane to come that close to MAPP gas!.
It certainly dosent even give 30% of the distance in my (crappy) gun.
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waxman
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Tried both propane and MAPP. Propane fires easier, and I can't get a comparable big blast from the MAPP. I've got to build a better gas controller.
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