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First Gun. Insight Wanted

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 Gun. Insight Wanted

Unread postAuthor: wanimal » Sat Jun 30, 2007 11:56 pm

I've wanted to build a Potato Cannon for a long time, but i've never really had the motivation to do so until today. I went to my friend's open house, where a couple of friends brought their cannons. I am a perfectionist, and like things to look nice. So naturally, it bothered me when I saw everyone in total awe at a couple of crudely-made spud cannons. So I want to show my friends up, and have the self-satisfaction of building something that shoots potatoes over 100 yards.

I have a general plan for a propane combustion, but need some insight from some veteran Spudders. I want to make this a hobby of mine, so any insight is appreciated.

First: How long and what diameter barrel should I use? Is schedule 40 the best?

Second: I plan on building the propane meter shown on BCArms, but what is the right psi to use?

Third: Is a ported barrel better?

Fourth: Is the piezio igniter better than a lantern igniter?

And finally: What is the best potato? I work in a grocery store, so I can special order some too.

Basically: I want to spend about 50 dollars and make a hunk of potatoey goodness hurl through the air as far as humanly possible with the allotted budget.

Thank you for reading this. Any insight, even opinionated would be greatly appreciated.
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Unread postAuthor: noname » Sun Jul 01, 2007 12:02 am

I'd use a foot of 3" Sch 40 PVC for the combustion chamber, and have a 1 1/2" PVC barrel about 4 or 5 feet long.
Once you have built the cannon, you can use online calculators (FuelTool, SpudTool) to find out what pressure you need in the propane meter.
A ported barrel doesn't help. However, if you shoot at night, you can get really cool muzzle flashes.
A piezoelectric BBQ igniter can be wired into multiple sparks, and you can put it in a cool handle. A lantern igniter is cheaper. It's up to you, though both will ignite the fuel mixture.
I don't think there is any "best potato." I just get 10 pound bags of russets every now and then for ammo.
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Unread postAuthor: wanimal » Sun Jul 01, 2007 12:09 am

Thanks. I think i'll use the BBQ igniter. I think i'll go for the ported barrel as well.
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Unread postAuthor: 666lucky693 » Sun Jul 01, 2007 12:11 am

if u want to show up ur friends make a pneumatic it will shoot way farther then their combustions will and they will be amazed
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Unread postAuthor: wanimal » Sun Jul 01, 2007 12:17 am

I want to make a pneumatic as well (Put my dads 55 gallon 220v air compressor to use), but I want one I can bring anywhere, not having to worry about if there will be an air compressor near by.
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Unread postAuthor: 666lucky693 » Sun Jul 01, 2007 12:26 am

o well u could use a cordless pump if u wanted to take it places
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Unread postAuthor: Hailfire753 » Sun Jul 01, 2007 12:26 am

Hey, congrats on wanting to make a spudgun!! I was in the same possition you are in, and had my interest sparked by wonting to one-up a friend. Two great sorces of info are AdvancedSpuds.com and the spud wiki (link on top of page). I myself made my first spudgun less than a week ago, and I posted it here:
http://www.spudfiles.com/forums/viewtop ... html#99834

As you can see, i'm not a "vetran spudder", but you are having the same experiance that I had, so just put your mind to the task.

I used a simple, cost effective design, called the Green Hornet, from AdvancedSpuds, on the Build Your Own page. Chose something do-able, then get a piece of graph paper and improve on it.

1. I recomend a 1.5'' barrel, Sch40. That is the most widely used material, as sch80 is more expensive, and (in most cases) the pipe would come apart at the joints before its capactity could be reached. The length depends on your chamber size. generally, you would want a Chamber to barrel ratio of 1.5:1, as it will achive verry good distance. A .8:1 ratio is most efficient, and quieter, and is generally used for powerful fuels.

2. not sure what you mean, because I did not use propane :lol:

3. Ported? excuse my lack of knowlege, but does that mean it has holes on the end? If so, It is only used for over-sized barrels or silencers, like mine. Otherwise, no idea.

4. depends. Lantern lighter is more dependable, but more auckward to fire. Use a grill lighter if you are going for a "cool" factor, or gun-like trigger.

5. The heaviest, roundest ones. Not sure of specific types though. Russet, mayby?

My gun cost less than 50, I had a fan, silencer, LED, breach loading, gun grips, and labels.... (That almost sounded like bragging, but I don't mean it to be.) However, i do not use propane - mine is a OUST "spray an pray". I advise doing a lot of research before even getting the materials, in any case.

EDIT - it sounds like the gun you are going for is more advanced than mine, so take my advice with a grain of salt.
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Unread postAuthor: wanimal » Sun Jul 01, 2007 12:31 am

I saw your gun earlier...amazing. I love the LEDs, and thanks for telling me about the Green Hornet.
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Unread postAuthor: Hailfire753 » Sun Jul 01, 2007 12:34 am

Yep, thanks, and good luck
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Unread postAuthor: SpudBlaster15 » Sun Jul 01, 2007 1:45 am

1) The general consensus seems to be that a 1.5" diameter barrel is best for spuds, though some prefer to use 2" barrels. The choice is up to you.

2) The proper meter pressure is dependent upon your meter volume, chamber volume, and fuel type. There are a number of free programs out there that will do the Math for you, but I suggest reading up about gas laws, and figuring out how to do it yourself. I am severely annoyed when someone builds a launcher without actually knowing how it works.

3) Porting the barrel is thought to increase the range and accuracy of the projectile by preventing the gases escaping from the end of the barrel from pushing the exiting projectile into a tumbling state.

4) Both will reliably ignite a proper fuel mixture, but grill igniters generally offer more diversity in terms of mounting positions and spark configurations. Lantern igniters will require the flint to be changed over time as it wears out, while a grill igniter should outlast the launcher. Although grill igniters are generally more expensive, they can often be salvaged from old grills for free. My friend and I jumped the electric fence at the local garbage dump, and managed to salvage a total of 15 igniters from grills people had dumped there.

5) Potatoes with a higher starch content will be denser, and will thus your slugs will have a greater mass, meaning more projectile energy. However, this difference will likely be small, and you should instead use the least expensive potatoes you can find, provided they are large enough in diameter to seal your barrel, and in good physical condition. Another aspect to consider is the shape of the potatoes. A potato whose thickness is similar to the diameter of the barrel will produce a more spherical slug when cut, making for a more aerodynamically stable projectile.

666lucky693 wrote:if u want to show up ur friends make a pneumatic it will shoot way farther then their combustions will and they will be amazed


Dude, cool it for a while. Every one of your posts that I have read has stated something to the effect of "Pneumatics are better than combustions". Aside from this being untrue in many cases, the original poster has already decided that he wants to build a combustion. So, please, if you have nothing to add in terms of advice, take your opinions elsewhere.
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Unread postAuthor: chaos » Sun Jul 01, 2007 2:17 am

just an idea here, maybe go for under and over style? perhaps (sorry if it has already been mentioned) metered propane setup for consistent shots/more power

hope all works out 8)
~chaos
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Unread postAuthor: blue2583 » Thu Jul 19, 2007 9:27 pm

good luck :lol:
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Unread postAuthor: frankrede » Thu Jul 19, 2007 10:09 pm

chaos wrote:just an idea here, maybe go for under and over style? perhaps (sorry if it has already been mentioned) metered propane setup for consistent shots/more power

hope all works out 8)
~chaos
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Unread postAuthor: chaos » Fri Jul 20, 2007 1:18 am

frankrede wrote:
chaos wrote:just an idea here, maybe go for under and over style? perhaps (sorry if it has already been mentioned) metered propane setup for consistent shots/more power

hope all works out 8)
~chaos
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its not that hard, just a little bit of research, and he might learn something
that would be useful to him in the future.
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Unread postAuthor: spudthug » Fri Jul 20, 2007 9:31 am

people have built huge asse piston valves for their first guns :wink:

if you use burntlatke, the wiki, and maybe advancedspuds, you can easily build a fuel meter, and a good combution/ pneumatic gun.

as for the protable pneumatic. the only possible way to make it portible is through c02/hpa or a bicycle pump.
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