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CPCII Revised, with action video

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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CPCII Revised, with action video

Unread postAuthor: Boom_erang » Mon Apr 28, 2008 9:44 am

Based on some cool info found on the forums, I shortened my chamber to make a .8:1 C:B and increased the size of the suppressor. It still has a bang, but it is quieter than before by quite a bit. And it's difficult to tell subjectively, but I'd say the potato comes out faster than before.

The spray and pray method has its shortcomings, as you all know, and I'm feeling that now. Been reading up on propane meters and I'm starting to work on a design. I think I'm aiming for more portable than something huge and awesomely powerful...

I also have an idea for a butane-powered (metered???) pill-bottle mini.

Anyway, the current gun's specs are:

48" barrel, last 12" drilled for suppression. So for the C:B ratio, I used 42" for the calculation. Chamber is 4" x 8" (shortened from 16"!!) although I forgot to include the volume of the handle in the calculation... I may fill the handle.

Ignitor is a standard CharBroil piezo, inserted directly into the chamber via the handle, and sealed with high-temp RTV.

Desert camo paint job with Krylon "Super Flat" Fusion spray paint, tan and brown.

[youtube]http://www.youtube.com/watch?v=khP1tQOq94U[/youtube]

I did a quick "damage video" today:

[youtube]http://www.youtube.com/watch?v=tRHRnNRWXs0[/youtube]
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PC_2-5_sm.jpg
Further modified simple combustion cannon with 4"x8" chamber and 42" barrel with suppressor.
Last edited by Boom_erang on Mon May 26, 2008 8:44 pm, edited 1 time in total.
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Unread postAuthor: ALIHISGREAT » Mon Apr 28, 2008 11:20 am

nice looking cannon, i like the paintjob :P
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Unread postAuthor: kostaki » Mon Apr 28, 2008 3:44 pm

I dont get the .8:1 c:b more power i thought the ideal ratio was 1.5:1
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Unread postAuthor: SpudFarm » Mon Apr 28, 2008 3:48 pm

1.5 : 1 is to give you a really nice BANG (i think)
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Unread postAuthor: kostaki » Mon Apr 28, 2008 3:50 pm

O its not the bang i want its the power to loud isnt always good (neighbors)
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Unread postAuthor: JDP12 » Mon Apr 28, 2008 4:14 pm

you want power... go .8:1 or a bad ratio and burst discs.. burst discs allow the pressure to build up some before they burst.
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Unread postAuthor: SpudFarm » Mon Apr 28, 2008 4:18 pm

ilovetoblowthingsup wrote:you want power... go .8:1 or a bad ratio and burst discs.. burst discs allow the pressure to build up some before they burst.

and that means you can use a shorter barrel...
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Unread postAuthor: kostaki » Mon Apr 28, 2008 4:18 pm

Thanks for the info ILTBTU and clearing that up next combustion .8:1 ratio
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Unread postAuthor: JDP12 » Mon Apr 28, 2008 4:36 pm

no problem... even if it isn't .8:1, i believe boogieman did some testing that showed using burst discs would improve the performance if it was a bad C:B ratio... look on http://www.advancedspuds.com somewhere for his testing with it.
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Unread postAuthor: Boom_erang » Mon Apr 28, 2008 4:47 pm

kostaki wrote:I dont get the .8:1 c:b more power i thought the ideal ratio was 1.5:1


Kostaki,

So did I, based mainly on info from Spudtech here: http://www.spudtech.com/content.asp?id=6.

However, after reading some of the threads here (I'm still a newbie, by the way), and especially after seeing the data here:

http://www.burntlatke.com/jpg600/15cb-graph.gif
http://www.burntlatke.com/jpg600/25cb-graph.gif
http://www.burntlatke.com/jpg600/cb-graph.jpg

And noticing that regardless of barrel diameter, the .7:1 or .8:1 ratio produces the most projectile speed.

Albeit this is for a metered propane system... But I suspect that for spray -n- pray guns, if the fuel mix is even close to optimum, that this ratio would still hold true. It certainly seemed to make a difference on mine!

-B
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Unread postAuthor: STHORNE » Tue Apr 29, 2008 5:13 pm

nice work. i love the paint job and thats one mighty silencer lol.

2 thumbs up!
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Unread postAuthor: bigbob12345 » Tue Apr 29, 2008 5:40 pm

Thats one puurty cannon
I really like the paint job, makes my painting look bad
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