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Long combustion chamber HELP

A place to ask general spud cannon related questions.
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Long combustion chamber HELP

Unread postAuthor: valentinesc » Mon Apr 09, 2012 9:28 pm

Hello: My scouts made a potato cannon using a plan they saw on the net. Well when they went shopping they bought the wrong size pipe for the chamber. Their combustion chamber is about 40" long. They are now trying to figure out where to put the BBQ ignitor that their going to use.
Should they put it about 1/2 way down the chamber or more towards the top of it.
They know they'll have to use more hairspray then average which doesn't bother them. They just want to know where to put the ignitor.
Thanks for any help.
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Re: Long combustion chamber HELP

Unread postAuthor: jackssmirkingrevenge » Mon Apr 09, 2012 11:48 pm

valentinesc wrote:Should they put it about 1/2 way down the chamber or more towards the top of it.


Towards the rear seems to be the ideal.

Some high speed footage of how the flame front propagates can be seen in this thread.

They know they'll have to use more hairspray then average which doesn't bother them. They just want to know where to put the ignitor.


Less is more with spray-and-pray type launchers, and they might want to add a mixing fan to help get a consisted fuel spread.
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Unread postAuthor: jsefcik » Tue Apr 10, 2012 1:47 pm

you can cut the chamber down if you need too,

if you wanna really get technical, put a chamber fan and use better fuel( carb cleaner or starting fluid)
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Unread postAuthor: jimmy101 » Tue Apr 10, 2012 7:59 pm

jsefcik wrote:if you wanna really get technical ,,, better fuel( carb cleaner or starting fluid)

Don't even let the kids f-around around with any kind of spray-and-pray setup! Teach'm to do it correctly.

A typical sized combustion spudgun has about the same muzzle energy as a 22 cal rifle. Would you even consider letting the scouts fiddle with the powder load in a rifle? Why in the world would you treat a spudgun any different? Even a simple combustion gun is potentially lethal.


Spend the $5 it would cost to meter the fuel with a syringe and actually teach the kids something. (Too little fuel and it won't fire, too much fuel and it won't fire, ... why is that? How much is the correct amount and why?)

The fuel meter will do a lot more to the performance of a combustion gun than will any other single improvement.

Second most significant improvement is a chamber fan. For a long chamber you either have to be patient (as in waiting several minutes between fueling and firing) or you have to have fan to speed mixing.
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Unread postAuthor: jsefcik » Tue Apr 10, 2012 9:49 pm

jimmy101 wrote:
jsefcik wrote:if you wanna really get technical ,,, better fuel( carb cleaner or starting fluid)

Don't even let the kids f-around around with any kind of spray-and-pray setup! Teach'm to do it correctly.

A typical sized combustion spudgun has about the same muzzle energy as a 22 cal rifle. Would you even consider letting the scouts fiddle with the powder load in a rifle? Why in the world would you treat a spudgun any different? Even a simple combustion gun is potentially lethal.


Spend the $5 it would cost to meter the fuel with a syringe and actually teach the kids something. (Too little fuel and it won't fire, too much fuel and it won't fire, ... why is that? How much is the correct amount and why?)

The fuel meter will do a lot more to the performance of a combustion gun than will any other single improvement.

Second most significant improvement is a chamber fan. For a long chamber you either have to be patient (as in waiting several minutes between fueling and firing) or you have to have fan to speed mixing.


never said not to treat the spudgun like a loaded gun

also depends on how old the scouts are as well,
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Unread postAuthor: Crna Legija » Wed Apr 11, 2012 1:27 am

lol i wouldn't let Jessie fiddle with the load of a .22 :D
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Unread postAuthor: DYI » Wed Apr 11, 2012 10:47 am

Position the ignition point near the rear of the chamber, behind the chamber fan (which, as Jimmy mentioned, is very important, especially with longer chambers). Use syringe based fuel metering unless you want a tool whose chief use is to frustrate the users.

Inject fuel, close chamber, turn on fan, fire, open chamber to vent. I can't add much of use to what Jimmy already said - proper metering is dirt cheap, dead simple, saves time and frustration, allows consistent performance, and serves as a learning opportunity. Don't bother with the spray'n'pray method.
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Unread postAuthor: jimmy101 » Wed Apr 11, 2012 11:42 am

jsefcik wrote:...never said not to treat the spudgun like a loaded gun

also depends on how old the scouts are as well,
Anyone using spray-n-pray is not treating a spud gun like a real gun, they are treating it like a toy or novelty.

Doesn't matter if the scouts are 6 or 17 there is an age appropriate way of teaching them how to use a gun properly.
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Unread postAuthor: jsefcik » Wed Apr 11, 2012 4:26 pm

jimmy101 wrote:
jsefcik wrote:...never said not to treat the spudgun like a loaded gun

also depends on how old the scouts are as well,
Anyone using spray-n-pray is not treating a spud gun like a real gun, they are treating it like a toy or novelty.

Doesn't matter if the scouts are 6 or 17 there is an age appropriate way of teaching them how to use a gun properly.


how the hell do you know they are treating it like a toy? i have my fun with my guns but im always safe when it comes to shooting it,
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Unread postAuthor: jsefcik » Wed Apr 11, 2012 4:28 pm

Crna Legija wrote:lol i wouldn't let Jessie fiddle with the load of a .22 :D



hahaha not, ive been shooting and reloading since i was 5 with my dad, im very well can safely operate and use my guns or spudguns in that matter, your prob the person not to trust
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Unread postAuthor: jimmy101 » Wed Apr 11, 2012 4:40 pm

jsefcik wrote:
jimmy101 wrote:
jsefcik wrote:...never said not to treat the spudgun like a loaded gun

also depends on how old the scouts are as well,
Anyone using spray-n-pray is not treating a spud gun like a real gun, they are treating it like a toy or novelty.

Doesn't matter if the scouts are 6 or 17 there is an age appropriate way of teaching them how to use a gun properly.


how the hell do you know they are treating it like a toy? i have my fun with my guns but im always safe when it comes to shooting it,
If you are fueling with spray-n-pray then you are treating it like a toy.

1. The chances of a miss-fire are high. Which prompts the shooter to loose focus and start pulling the trigger repeatedly. Sometimes the gun will fire on the fifth trigger pull, by which time the muzzle may not be pointing downrange.

2. Most shots from spray-n-pray will have a small fraction of the power the gun is capable of. Then you randomly get a fueling that is actually correct and the muzzle energy goes up 10 fold. No self respecting serious shooter would consider firing a gun with that much variability. It is unsafe.

3. You are working with kids (be they 5 yo or 17 yo), do it right or don't do it at all. The spudding community really doesn't need a kid scout getting hurt because the "responsible adult" wasn't.
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Unread postAuthor: jsefcik » Wed Apr 11, 2012 8:33 pm

No 5 trigger pulls with a flint sparker=)


How do you know spray and prays are all treated like toys??

Do you watch everybody who has one?? To make sure they ate playing with it like a toy??

Unless you have a video of everybody who has one treating it like toy hush up :shock:
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Last edited by jsefcik on Thu Apr 12, 2012 10:25 am, edited 1 time in total.

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Unread postAuthor: Lockednloaded » Wed Apr 11, 2012 8:54 pm

jsefcik wrote:No 5 trigger pulls with a flint sparker=)


Hoe do you know spray and prays are all treated like toys??

Do you watch everybody who has one?? To make sure they ate playing with it like a toy??

Unless you have a video of everybody who has one treating it like toy hush up :shock:


You can't be serious... He just gave 3 clearly stated reasons
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Unread postAuthor: Crna Legija » Thu Apr 12, 2012 1:44 am

jsefcik wrote:im very well can safely


lol that sure makes me feel better. :D





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Unread postAuthor: jimmy101 » Thu Apr 12, 2012 5:20 pm

jsefcik wrote:No 5 trigger pulls with a flint sparker=)

How do you know spray and prays are all treated like toys??

Do you watch everybody who has one?? To make sure they ate playing with it like a toy??

Unless you have a video of everybody who has one treating it like toy hush up :shock:
Wrong again. You're batting near 1000. The misfire is not caused by the spark, it is caused by not having a combustible mixture at the spark.

If you fuel with spray-n-pray for more than your first couple shots with your first cannon you are just joking around. Might as well throw the spud for all the performance you are getting. You're just going for the "bang".
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