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Combustion chamber below barrel for repeating cannon?

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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Combustion chamber below barrel for repeating cannon?

Unread postAuthor: Cthulhu » Wed Apr 12, 2017 7:13 pm

Hi, I'm new to the forum, so if I make any mistakes please tell me.

I have built a simple combustion cannon before, but after watching Grant Thompson's YouTube video with the "Sonic blast cannon" I became amazed at the ability to use a sponge fuel cell to get repeated shots.

However, I disliked that you have to remove the barrel entirely to load in a new projectile, so here's my question: can you place the combustion chamber below the barrel (connected by a PVC T joint perhaps)?
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Re: Combustion chamber below barrel for repeating cannon?

Unread postAuthor: jrrdw » Thu Apr 13, 2017 7:45 am

Yes, you can configure a cannon any way you want but the question of performance will always be there until you build and test it.

That is par for course with every cannon, built by any builder. When it comes to builders, practice makes almost perfect!

Welcome to Spudfiles. :mrgreen:
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Re: Combustion chamber below barrel for repeating cannon?

Unread postAuthor: WizardNoodle » Thu Apr 13, 2017 8:13 am

Cthulhu wrote:Hi, I'm new to the forum, so if I make any mistakes please tell me.

I have built a simple combustion cannon before, but after watching Grant Thompson's YouTube video with the "Sonic blast cannon" I became amazed at the ability to use a sponge fuel cell to get repeated shots.

However, I disliked that you have to remove the barrel entirely to load in a new projectile, so here's my question: can you place the combustion chamber below the barrel (connected by a PVC T joint perhaps)?


You most definitely can. This type of cannon build is typically referred to as an "over/under."

The basic combustion version of this would be the chamber attached to an elbow, with a short(4" length) pipe into the other end of the elbow. Then attach an elbow to the other end of the 4" pipe and then depending on your barrel size, a reducer.

However in your design for how the ammunition will feed into the barrel, keep in mind that any space of air not directly in the barrel or chamber is a waste and will negatively affect your cannon's performance. To combat this I recommend some sort of spring seal system where a spring is attached to the top of the magazine and a cut piece of material that will mostly seal the magazine as it is constantly pushing down on the ammunition, maybe a round block of plywood and an O-ring around it or just a round piece of rubber gasket that fits perfectly + 0.1 inch into the magazine. This way the combustion doesn't fill up dead space and goes down the barrel like it's supposed to :wink:

Welcome to Spudfiles, and good luck on your project!

PS, I would also look at Performance Cannons for some inspiration on how powerful these things can go ;)
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Re: Combustion chamber below barrel for repeating cannon?

Unread postAuthor: Cthulhu » Thu Apr 13, 2017 9:16 am

Thanks so much on the info, the breech for the projectiles will be a PVC interrupted screw that has a de bange interruptor for an airtight seal, my only concern is the space between the breech and combustion chamber.
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