Whats your favortite fuel?

[vng21092]

Would you guys recommend butane? Or propane? Or something else...

[jrrdw]

Farts in a can! Try everything you can get your hands on...

[jackssmirkingrevenge]

Take your pick

[vng21092]

I was reading up on the use of chamber fans, do they really make a significant difference? Also, does having a chamber fan remove the necessity of an injection port? The fan would just suck in the fuel right?

[PeteS]

I was reading up on the use of chamber fans, do they really make a significant difference? Also, does having a chamber fan remove the necessity of an injection port? The fan would just suck in the fuel right?

In my experience, yes they make a significant difference and no they do not remove the necessity of an injection port.

[vng21092]

so my chamber is 1 1/4 pipe x 6 inches, the volume is 7.36 inches which equals .121 liters, which is 121 ml? so I'm suppose to be using (3/100) * 121 = 3.63 ml of butane? why do I have a feeling that is completely wrong

[PeteS]

so my chamber is 1 1/4 pipe x 6 inches, the volume is 7.36 inches which equals .121 liters, which is 121 ml? so I'm suppose to be using (3/100) * 121 = 3.63 ml of butane? why do I have a feeling that is completely wrong

Check your measurements. If it is 1-1/4" schedule 40 pipe the actual ID is 1.38". It looks like you assumed 1.25".

If it is schedule 80 then it is more like 1.278" ID.

Actually if you want a good measurement of the volume, you might want to measure how much water it takes to fill the chamber. That avoids calculation errors and takes into account the shape of fittings and what not.

[vng21092]

can you help me calculate how much butane I should be using?

[PeteS]

can you help me calculate how much butane I should be using?

It looked like you did everything right, except for what looked like an incorrect assumption about the inside diameter of the chamber.

Assuming 6" of 1-1/4" schedule 40 pvc, it comes to a chamber volume of 8.97". Are you using 1-1/4" schedule 40? Also, there could be variations for fittings or whatever, but counting just the pipe 8.97" it is. That comes to 147 ml. Three percent of that is 4.41 ml. If I didn't make any errors and my assumptions about your gun are correct, that should do it.

If your chamber has other nooks and crannies the volume calculation may need to be redone to include them. That or fill it with water and measure how much water it takes.

[vng21092]

yup its schedule 40,I'm an idiot and I bought a 100 ml syringe, so using 4.4 makes the plunger move up barely 1/4 inch, that is why I thought I was off by a lot, but thanks for the help, I'm gonna see if I could get it to fire tomorrow

[PeteS]

Good luck and keep us posted on how it goes. Also be careful.

BTW, if you have any issues with ignition the two most likely causes that I have seen are a spud that didn't seal the barrel off and poor fuel/air mixing. If you have fuel/air mixing issues, putting something in the chamber that can mix it up when shaken helps. I have used a plastic bottle cap. Fans are nice for mixing, but you can get by without.

[vng21092]

ALRIGHTY guys I've got some pics, I was really inspired by this post http://www.spudfiles.com/combustion-can ... 25490.html, the idea of being able to disassemble the gun was very appealing so I went with that approach

My gun is separated into three parts: stock, firing chamber+short barrel, extended barrel, all in all the length of each piece is ~14 inches which is great since they can easily be packed inside a book bag.


The gun should double both as a shotgun and a sniper


Injection port is a 1 1/4 plug with a 1/4 rod coupling epoxyd onto it, its plugged with a 1/4 bolt of course


Loading is through a breech in the barrel, a 1/2 coupling with the inside dremeled out can slide over the breech hole


I still haven't gotten the first shot out yet, I assume its because the air + fuel mixture is bad, but the spark works, thanks for all the help guys and I will get a damage video when I finally get it working

[PeteS]

I still haven't gotten the first shot out yet, I assume its because the air + fuel mixture is bad, but the spark works, thanks for all the help guys and I will get a damage video when I finally get it working

Likely because the chamber volume used in the calculation needs to include the nipples, elbows, and fittings all the way up to the spud unless there is a burst valve or something before that.

Nice looking gun.

[jimmy101]

so my chamber is 1 1/4 pipe x 6 inches, the volume is 7.36 inches which equals .121 liters, which is 121 ml? so I'm suppose to be using (3/100) * 121 = 3.63 ml of butane? why do I have a feeling that is completely wrong

For those dimensions that is the correct amount of fuel.