Spud gun disguised as classic artillery

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.
RLI3CDO
Recruit
Recruit
United States of America
Posts: 1
Joined: Fri Jun 03, 2022 7:18 am
Been thanked: 2 times

Fri Jun 03, 2022 8:40 am

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.
Attachments
20220602_033015.jpg
20220602_182437.jpg
20220603_083038.jpg
20220603_083049.jpg
20220603_084850.jpg
20220603_084904.jpg
User avatar
jrrdw
Moderator
Moderator
United States of America
Posts: 6554
Joined: Wed Nov 16, 2005 5:11 pm
Location: Maryland
Has thanked: 22 times
Been thanked: 11 times
Contact:

Donating Members

Sat Jun 04, 2022 4:19 am

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. :mrgreen:
User avatar
D_Hall
Staff Sergeant 4
Staff Sergeant 4
United States of America
Posts: 1891
Joined: Thu Feb 07, 2008 7:37 pm
Location: SoCal
Has thanked: 5 times
Been thanked: 25 times

Donating Members

Mon Jun 06, 2022 10:42 pm

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).
Simulation geek (GGDT / HGDT) and designer of Vera.
User avatar
D_Hall
Staff Sergeant 4
Staff Sergeant 4
United States of America
Posts: 1891
Joined: Thu Feb 07, 2008 7:37 pm
Location: SoCal
Has thanked: 5 times
Been thanked: 25 times

Donating Members

Thu Jun 09, 2022 10:35 pm

jrrdw wrote:
Sat Jun 04, 2022 4:19 am
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. :mrgreen:
Percussion caps are sufficient for lighting solid fuels on fire. They'll do just fine in a spud gun.
Simulation geek (GGDT / HGDT) and designer of Vera.
User avatar
jrrdw
Moderator
Moderator
United States of America
Posts: 6554
Joined: Wed Nov 16, 2005 5:11 pm
Location: Maryland
Has thanked: 22 times
Been thanked: 11 times
Contact:

Donating Members

Sat Jun 11, 2022 1:26 pm

D_Hall wrote:
Thu Jun 09, 2022 10:35 pm
jrrdw wrote:
Sat Jun 04, 2022 4:19 am
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. :mrgreen:
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
Sergeant Major
Sergeant Major
United States of America
Posts: 3189
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Has thanked: 1 time
Been thanked: 11 times
Contact:

Mon Jun 13, 2022 3:06 pm

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")
Image
User avatar
jackssmirkingrevenge
Five Star General
Five Star General
Posts: 26011
Joined: Thu Mar 15, 2007 11:28 pm
Has thanked: 388 times
Been thanked: 214 times

Donating Members

Thu Jun 16, 2022 8:24 am

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?
hectmarr wrote:You have to make many weapons, because this field is long and short life
Post Reply