A new look at combustion cartridge Spud guns

Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
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Cthulhu
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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?
This weapon serves to silence the noisy speakers of the stupid of the other street! (joke) -Hectmarr
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D_Hall
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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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Simulation geek (GGDT / HGDT) and designer of Vera.
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jackssmirkingrevenge
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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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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Cthulhu
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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.
This weapon serves to silence the noisy speakers of the stupid of the other street! (joke) -Hectmarr
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Cthulhu
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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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Tue Jun 13, 2017 10:57 am

Butane, propane, methane, ... are all essentially identical:
http://www.inpharmix.com/jps/Combustion_fuels.html
spud_wiki/index.php?title=Common_Fuels_ ... n_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%20Met ... ghter.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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Mon Aug 21, 2017 9:12 pm

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Cthulhu
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Tue Aug 22, 2017 4:50 am

thunderskunk wrote:CThulhu,

Something like this?

http://www.spudfiles.com/combustion-can ... 25895.html
Wow! That's a very similar project indeed!
I'll definitely look at it for some info as I work.
This weapon serves to silence the noisy speakers of the stupid of the other street! (joke) -Hectmarr
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Sat Nov 16, 2019 12:42 am

Ok so being the stubborn guy that I am, I'm back at this again.
This time I have multiple successful combustion guns under my belt and I actually know how to use HGDT :lol:
Here's a really crappy animation I made showing my idea (sorry for the bad lighting and the rapid speed, still learning):
[youtube][/youtube]
The body of the cartridge is 2 inch PVC pipe that's 15 inches long. The base of the cartridge holds a screw that doubles as an ignition electrode as well as a fueling port along with another electrode that is attached to a washer (to make the cartridge symmetric and easy to fire). The top of the cartridge has a permanently installed disc upon which an aluminum foil burst disk is placed. Over this, the second half of the burst disk assembly fits on with 8 screws and is sized to hold a golf ball (or any other 1.68 inch diameter projectile).
GBCartridgeHGDT.PNG
Not amazing performance but pretty good for being on a budget! HGDT did show an abnormal increase in power just from slightly strengthening the burst disk but I'm hoping this will happen in the real world.

The debate now turns to what to make the cartridge base/fueling port/electrode holder and the burst disk holder out of. I could fiddle with dimensions and 3d print them or I could cast some epoxy resin into cylinders roughly the diameter of the pipe and turn them on my wood lathe, not sure which would function better :?
This weapon serves to silence the noisy speakers of the stupid of the other street! (joke) -Hectmarr
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hectmarr
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Sat Nov 16, 2019 4:06 pm

The debate now turns to what to make the cartridge base/fueling port/electrode holder and the burst disk holder out of. I could fiddle with dimensions and 3d print them or I could cast some epoxy resin into cylinders roughly the diameter of the pipe and turn them on my wood lathe, not sure which would function better :?
I think what is missing is in this drawing of Jack. The truth, and after giving a few turns in my head to the issue of a hybrid cartridge, the design with rupture disc is the best. It solves the retention aspect of the compressed mixture, solves the regulation of the pressure peak, solves the ability to use a magazine with several cartridges inside and use as a repetitive firearm, without needing a dispenser, air tank, valves etc, on board of the weapon It is a proven and viable technology, and not much technical complexity to manufacture.Besides, you can throw pellets, bbs, and any projectile of the caliber one has.
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Ideas don't make holes. The weapons yes! ;)
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