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Cooling Down the Gun

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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Cooling Down the Gun

Unread postAuthor: Saboo » Thu Aug 30, 2007 9:09 pm

I have a combustion gun that requires petrol to fire a small home made pellet that lots like a penut into quarter inch copper pipe. What methods of cooling down the gun could you suggest. The gun heats up after one shot and a wet towel doesnt work, neither does air cooled
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Unread postAuthor: FeLeX » Thu Aug 30, 2007 9:16 pm

Post some pictures because I have a very hard time imagining your gun.
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Unread postAuthor: Saboo » Thu Aug 30, 2007 9:26 pm

My gun, melted. I have no pictures of it. But it was just copper pipe, protruding from a cylinder at the end. The cylinder had a spark plug attached to the interior wich, ignited the petrol fumes. Unfortunatley, i was not too sure how much petrol to put in, this caused the barrel to heat up like a mother licker after a few shots. (hence this post)
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Unread postAuthor: jimmy101 » Fri Aug 31, 2007 12:07 pm

If you are generating enough heat to melt copper pipe than I would say that your chamber is way too big for the barrel.

Over fueling is a possibility, but the gun shouldn't fire at all with more than ~2x as much as fuel as the stoichiometry predicts.

Heck, a real gun can be fired many times without warming the barrel anywhere near the melting point of copper. So there is something seriously wrong with the design of your gun.

Are you putting in so much fuel that only a tiny amounts vaporizes, that small amount is ignited, the projectile leaves the barrel, fresh air is drawn back into the gun and the gross excess of liquid fuel is then ignited?

Check the SpudCom page on liquid fuels to get an idea of how much fuel is needed. IIRC, a typical sized gun would only use a few drops of gasoline as fuel.
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Unread postAuthor: Blackett » Mon Sep 03, 2007 1:49 pm

I cant think of why that would happen unless your doing something crazy involving thermite.

my suggestion would be to use some other fuel. I am not sure how you are getting the petrol fumes, but I think you may be actually leaving some liquid in there which continues to burn after the several nanosecond combustion.

I dont know what your chamber was made of either, just a few more details would be cool and we csn figure how to have this not happen anymore.
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Unread postAuthor: thespeedycicada » Mon Sep 03, 2007 1:58 pm

how did you manage to melt copper please tell me i really want to know so i can try it.Or did the chamber melt? if so what was it made of? I dont think you could melt copper with petrol unless you used a blast furnace mabey im wrong i am no expert but i have a hard time beleiving you melted copper pics would be nice.
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Unread postAuthor: meatballs » Fri Sep 07, 2007 3:39 pm

pvc and abs have much lower melting points than copper and they dont melt when used in spudguns so i dont see how copper could possibly be melting just from shooting. please please please give more info on the gun, im really confused, are you shooting into copper pipe with your peanut like projectile or is that the barrel? what was your melted chamber made from? how much fuel were you using? gun dimentions? anything?
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Unread postAuthor: Saboo » Tue Sep 18, 2007 7:28 pm

The whole gun melted. More of an explosion than melting. The copper is pretty mangled and some of its quite !$@#%@. I filled the whole chamber with petrol :oops:
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Unread postAuthor: Blackett » Tue Sep 18, 2007 8:18 pm

well thats a self explanatory no no.

well at least you know what not to do by now.
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Unread postAuthor: TwitchTheAussie » Tue Sep 18, 2007 9:14 pm

Yep. No more petrol for you *takes petrol can* :D
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Unread postAuthor: jimmy101 » Wed Sep 19, 2007 11:27 am

OK, we'll let you use petrol, but you'll have to take a signed check out slip to the stockroom. You'll receive your petrol in lots of 5 drops. Enough to fire a reasonable size gun, at full power, once.
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Unread postAuthor: Fnord » Wed Sep 19, 2007 12:48 pm

The whole gun melted. More of an explosion than melting. The copper is pretty mangled and some of its quite !$@#%@. I filled the whole chamber with petrol


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(If by petrol, you mean gunpowder, I believe you. If you mean gasoline/petroleum/diesel, pictures or it didn't happen.)
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Unread postAuthor: williamfeldmann » Wed Sep 19, 2007 1:29 pm

What would even make someone think that lighting a chamber full of gasoline would be a good idea (for propulsion anyway, you firebugs :D). I mean the liquid form burns for quite some time and doesn't explode in normal atmosphere or pure oxygen environment until it is under some pretty decent pressure. If this is just a regular combustion gun it wouldn't be under pressure or in apure oxy environment.

Even gunpowder wouldn't have blown the gun up unless the copper was the weakest point, and I mean weaker than the seal and friction between the barrel and projectile, and there a good chunk of blackpowder in the gun. I have a copper cannon (true cannon, like napoleanic) that uses 200 grain loads to shoot cement filled pingpong balls and it doesn't even heat up to where I can't touch it.
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Unread postAuthor: Killjoy » Wed Sep 19, 2007 1:31 pm

I cant think of why that would happen unless your doing something crazy involving thermite.


haha I did that with a pvc cannon, good time good times.

You could try hitting it for a second or two with a co2 fire extinguisher, or build some sort of heatsink out of aluminum or copper.
But without pictures, there is a slight smell of bs is in the air.
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Unread postAuthor: mega_swordman » Wed Sep 19, 2007 2:31 pm

Do what they did in WW1 and pee on the barrel :D. Either way, filling the chamber with gasoline (regardless if it is true or not) seems like a pretty good way to prove you lack the common sense required for this project. Think before you act and don't let friends influence your judgement.
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