Spud gun disguised as classic artillery

[RLI3CDO]

I am attempting to build spud cannons that closely resemble historic field artillery and naval deck guns circa 1860 - 1940. My first attempt is a British 12 pounder as built by The Elswick Ordnance Works in 1891. I am so far happy with the looks, but she will not fire. I have tried a variety of aerosol propellants, timing my spray into the chamber between 1 to 15 seconds. The specs on the gun are 2" bore x 40" length, runs through 3" tube into 4" chamber which is 18". The trunnion/s is a one piece 2" tube that passes through the 4" chamber with holes drilled through the trunnion inside the chamber. I am using a device that fires a percussion cap into the chamber. I enlarged the hole in the nipple and have confirmed I am getting a good 4" spark/flame into the combustion chamber. Is the chamber to large?, trunnion passing through chamber? any advice will be greatly appreciated. See attached images.

[jrrdw]

The " percussion cap" you're using probably works as intended for it's intended use. However, you're trying to ignite a fuel air mixture and will need a hotter, faster spark. Also a mixing fan would help greatly to mix the fuel and air and to clear the chamber after shots. Use a gas grill igniter for your ignition source.

Welcome to Spudfiles.

[D_Hall]

As far as I'm concerned....

If you're using hair spray or any other "aerosol" that isn't intended for burning, you've failed to do any meaningful research on the topic of spud guns.

DITCH THE DAMNED "AEROSOL PROPELLANTS"!

Propane. In a pinch, butane. If you find yourself in a 3rd world country with no other possibilities, ether. Anything else is just plain ignorant.

AAAAAAAAAAAAAARRRRRRRRRRRRRRRRGGGGGGGGGGGGGHHHHHHHHHHHHHH!!!!!!!!!!!!!!!

[A few deep breaths later]

Seriously, make a propane metering pipe. Do it right. If you're worried about the aesthetics, you can make the metering pipe detach before firing.

That said? Otherwise absolutely beautiful work.

One question though... Where are you finding your percussion caps? As one who recently built an inline cap & ball AR-15 (yes, seriously), I've found the caps impossible to find for sale (fortunately I had a few lying around the house).

[D_Hall]

The " percussion cap" you're using probably works as intended for it's intended use. However, you're trying to ignite a fuel air mixture and will need a hotter, faster spark. Also a mixing fan would help greatly to mix the fuel and air and to clear the chamber after shots. Use a gas grill igniter for your ignition source.

Welcome to Spudfiles.

Percussion caps are sufficient for lighting solid fuels on fire. They'll do just fine in a spud gun.

[jrrdw]

The " percussion cap" you're using probably works as intended for it's intended use. However, you're trying to ignite a fuel air mixture and will need a hotter, faster spark. Also a mixing fan would help greatly to mix the fuel and air and to clear the chamber after shots. Use a gas grill igniter for your ignition source.

Welcome to Spudfiles.

Percussion caps are sufficient for lighting solid fuels on fire. They'll do just fine in a spud gun.

In a moister enriched fuel environment? I respectfully disagree kind sir.

[jimmy101]

Gaseous fuels are usually pretty picky on the ratio being correct.

For propane the combustion limits is about 3% to about 8% propane to air by volume. Outside that range the fuel-air wont ignite regardless of your ignition source.

A meter pipe is perhaps the most elegant approach but overly complicated if the chamber volume is small enough. Up to about two liters of chamber volume you can use a syringe. You can get a 70cc syringe at an animal supply house for $2. Add another 2$ bucks for some blunt needles. Easy enough to fill the syringe from either a butane source (even a cheap butane lighter) or from say a Bernzomatic propane tank.

You can inject into the chamber through a hole sized to the syringe needle. A 1X combustion gun generates so little pressure that you can just cover the injection hole with a piece of tape after fueling.

spud_wiki/index.php/Fuel_meter


Syringes:

(or just search for "100ml syringe")

[jackssmirkingrevenge]

That is some beautiful work, excellent job!

I second the advice to properly meter fuel and as to ignition, instead of a percussion cap perhaps you can use the same hammer to strike a piezo that will generate a spark?

[mark.f]

Good work! Somebody already posted the video on syringe fueling I would go with that if you aren't willing to build a traditional "meter."
The percussion cap will ignite a good mix but a piezo igniter would be a lot more convenient in the long run I believe.