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A new look at combustion cartridge Spud guns

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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Re: A new look at combustion cartridge Spud guns

Unread postAuthor: Cthulhu » Sat Jun 03, 2017 8:18 am

D_Hall wrote:Or do you have a lot more friends than I think you do


Well it's actually my schools Spud gun club, so it's about 50 members. I agree though, "nearly infinite" is an over statement.

jackssmirkingrevenge wrote: I would go with 2" barrel and 3" cartridges.


Might look funky with the over sized cartridges for an undersized barrel, but I could probably do some stuff to make it a bit more aesthetic. Would making the cartridges 2" but long help or would they need to be absurdly longer to get good performance?
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Re: A new look at combustion cartridge Spud guns

Unread postAuthor: D_Hall » Sat Jun 03, 2017 5:03 pm

Cthulhu wrote:Might look funky with the over sized cartridges for an undersized barrel,


Any stranger than this example of an over sized cartridge with an undersized barrel/projectile?

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Re: A new look at combustion cartridge Spud guns

Unread postAuthor: jackssmirkingrevenge » Sun Jun 04, 2017 7:03 am

Cthulhu wrote:Might look funky with the over sized cartridges for an undersized barrel, but I could probably do some stuff to make it a bit more aesthetic. Would making the cartridges 2" but long help or would they need to be absurdly longer to get good performance?


I don't think this is a bad look (57mm recoilless rifle)

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Re: A new look at combustion cartridge Spud guns

Unread postAuthor: Cthulhu » Sun Jun 04, 2017 11:51 am

Well, it's not that it would look bad, but that it would look odd for the style I'm going for (British 18 pounder field cannon).

I think I may go with the 3" smooth bore simply for the increased strength of a larger cartridge and the real life dimension of the actual cannon.

I'll post my blueprints soon for criticism and suggestions.
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Re: A new look at combustion cartridge Spud guns

Unread postAuthor: Cthulhu » Tue Jun 06, 2017 10:17 am

Here are the rough (I repeat: rough) tentative blueprints. The main area of interest is the chamber for the round, which is composed of 3 couplers that have been sanded out on the inside to accept a 3" cartridge smoothly. To increase the strength of these couplers they are attached by 4 punched metal bars with screws binding it all together. It is from these punched bars that mock recoil assembly and elevation system are attached.

As for the breech, it's a simple wooden flap attached to a hinge on the side of the last coupler with a simple latch to lock it in place. The only really neat thing about it is the ejector, which is a curved piece of wood that enters a slot in the PVC when the breech is fully opened, gripping the cartridge rim and pushing it out enough to be grabbed.

I don't really like the current chamber design as it seems quite finicky, but it will provide a much more precise fit than a 4" PVC and adaptor.
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Re: A new look at combustion cartridge Spud guns

Unread postAuthor: jimmy101 » Tue Jun 13, 2017 10:57 am

Butane, propane, methane, ... are all essentially identical:
http://www.inpharmix.com/jps/Combustion_fuels.html
https://www.spudfiles.com/spud_wiki/index.php?title=Common_Fuels_for_Combustion_Spudguns

As Dave said early on, the ONLY thing that really matters in terms of fuel is getting the right amount in the gun. It is easy to build a meter for either propane of butane. A long handled butane lighter in particular is easy to mate with a syringe.
http://www.inpharmix.com/jps/Fuel%20Meter%20From%20A%20Disposable%20Butane%20Lighter.html
http://www.inpharmix.com/jps/Hacking_lighter.html

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The piezo ignitor in the lighter can also be used as the ignition system for the gun.

Or, you can use a butane lighter;
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Or, you can use a propane torch;
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Or you can use a propane or butane lighter refill cartridge;
https://www.youtube.com/watch?v=EoVDuh3ziNg

You can get 70cc syringes (good for propane up to a chamber volume of about 1.75L)at most farm supplies stores for a buck or so. The store will also have syringe needles.
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Re: A new look at combustion cartridge Spud guns

Unread postAuthor: thunderskunk » Mon Aug 21, 2017 9:12 pm

CThulhu,

Something like this?

combustion-cannon-database/topic25895.html
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Re: A new look at combustion cartridge Spud guns

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Re: A new look at combustion cartridge Spud guns

Unread postAuthor: Cthulhu » Tue Aug 22, 2017 4:50 am

thunderskunk wrote:CThulhu,

Something like this?

combustion-cannon-database/topic25895.html


Wow! That's a very similar project indeed!
I'll definitely look at it for some info as I work.
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