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propane gun

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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propane gun

Unread postAuthor: alabama mike » Wed Jul 27, 2016 9:18 am

Ok, my plan is to build basically a propane fired musket, 36 inch long 1/2 copper pipe as the barrel, and 2 inch pvc chamber, I have an old stun gun for ignition, and I ran by Radio shack yesterday and bought a fan that will fit in the 2 in pvc pipe. I went on the burnt lakes site and their calculator only goes down to 3/4 inch barrel so I'm currently doing the math to get my chamber and barrel to the 1.5 to 1 that is suggested.. Just wondering has anyone else on here tired a set up like this before and if so could you share any pointers you may have run across. with no rifling in the barrel my expectation would be a 20 to 30 yard gun.

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Last edited by jrrdw on Wed Jul 27, 2016 4:35 pm, edited 1 time in total.
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Re: propane gun

Unread postAuthor: jackssmirkingrevenge » Wed Jul 27, 2016 6:42 pm

You're not going to get an enormous amount of power, combustions provide fairly low pressure and having a larger caliber usually makes up for that, but with a 1/2" barrel it's going to be quite limited.

Consider downloading HGDT to estimate performance and play with the variables.

Note that a copper pipe will absorb more heat than a polymer one, meaning you will lose some power on that front too.
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Re: propane gun

Unread postAuthor: alabama mike » Thu Jul 28, 2016 11:47 am

jackssmirkingrevenge wrote:You're not going to get an enormous amount of power, combustions provide fairly low pressure and having a larger caliber usually makes up for that, but with a 1/2" barrel it's going to be quite limited.

Consider downloading HGDT to estimate performance and play with the variables.

Note that a copper pipe will absorb more heat than a polymer one, meaning you will lose some power on that front too.


Thank you for the reply, I tried to download the HGDT but seems there is a problem, all I get is a run time error. If you do a search on you tube for alcohol gun maybe you will get a better understanding of what I am wanting to accomplish. They seem to be used more in Philippines, Vietnam (that general area of the Pacific rim). only I want to update it by using a fanned chamber and propane instead of denature alcohol.

Now something I'm not understanding, how will the use of a copper pipe loose power? once the combustion has taken place in the chamber, my thinking would be the barrel material wouldn't matter, escaping gas is escaping gas, right?
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Re: propane gun

Unread postAuthor: jimmy101 » Fri Aug 05, 2016 11:38 am

All of the energy in the gases are in their temperature and heat. Heat loss to the chamber and barrel are pretty significant, particularly when you don't have all that much heat to start with. Indeed, in terms of density the combustion gases are actually at lower density once the ammo starts to move so all of the pressure is from the temperature. (In a pneumatic the pressure comes from increased gas density, in a combustion the pressure comes from increased temperature and offsets the actual decrease in gas density.)
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Re: propane gun

Unread postAuthor: mark.f » Fri Aug 05, 2016 4:25 pm

The performance won't be too spectacular, as others have mentioned, but 20-30 yards is perfectly doable...

Also, this post shows a number of the designs you are talking about, for a quick performance "run-down".
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Re: propane gun

Unread postAuthor: alabama mike » Wed Aug 10, 2016 10:09 am

Thanks guys for the replies, I've gotten everything together, But I believe the metering system must be off, I used the calculators on the Burnt Latke site, but I believe I'm over fueling. I Built it according the what the calculators say and I'm getting hit and miss ignition, I can hear the stun gun going off but its only firing one out of 10 times.
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Re: propane gun

Unread postAuthor: alabama mike » Wed Aug 10, 2016 10:12 am

mark.f wrote:The performance won't be too spectacular, as others have mentioned, but 20-30 yards is perfectly doable...

Also, this post shows a number of the designs you are talking about, for a quick performance "run-down".


Yes, those are some that I have gotten ideas from, my thought would just be to add a metering system and do away with the denatured alcohol. only differance Is I'll be shooting a lead ball instead of a marble.
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Re: propane gun

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Re: propane gun

Unread postAuthor: jackssmirkingrevenge » Sat Aug 13, 2016 5:43 am



Syringe Fuel Metering is your friend, especially for smaller launchers.

I'll be shooting a lead ball instead of a marble.


I'm afraid your muzzle velocity is going to be pretty miserable with a 1x combustion.
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