Need some help on chamber length...

[Fight The Machine]

Hi everyone,
I am new to this site, and have recently become interested in spud guns, so I read most everything on this site, and started to design my first cannon. My question is, I have designed a gun with a 4" diameter chamber, 18" long, and with a 1.5" diameter barrel, using the banjo fittings breech loading setup, but what should my total barrel length be to get the best shot? I plan on using right gaurd as fuel and two bbq ignitors as igniton. Any suggestion will be appreciated! Thanks, and sorry I have no picture or diagram to explain, my brainchild is currently just a blueprint on my desk.

[spudshot]

your chamber's volume should be 1.5 times your barrel's volume. how are you gonna use 2 bbq ignitors at the same time? you'd be better off using one, but wiring multiple sparks

[boilingleadbath]

For best preformance with that chamber, you'd want a barrel about 8-16 feet long, depending on who you ask.
However, don't make a smaller chamber if your only critera is power. Smaller chamber always* = less power.

As to the 2 bbq ignighters, you won't be able to press them close enough to the same time - the entire combustion is over in like a 60/th of a second.

[Fight The Machine]

Ok, I was thinking the two bbq ignitors are side by side with some fitting over the buttons, that when you push the fitting both ignitors spark, would this work?
__
I I

I = bbq ignitor button
__ = fitting over the buttons

I hope that gets my idea across, anyway, I have no way of knowing chamber or barrel volume as I have yet to buy any materials, and I wanted to know the barrel length to know how much pipe I will need.

[spudshot]

why? it'll cost you 30 bucks for the ignition, you can use 4 screws, a piece of wire, and one ignitor to make 2 sparks

[Fight The Machine]

Ok, now I agree with losing the double ignitor, it really just gave me an excuse to put more dohickeys on my gun, I'm still lost on the whole barrel length, is there anyway I can figure it out using the ratio without knowing the exact volume, all I know now is the diameter and length of the chamber, and that I want the barrel diameter to be 1.5".

[boilingleadbath]

For goodness sake, how hard is it to calculate volume?!
(2*2*pi*18 )=c volume of the chamber
(.75*.75*pi)=a area of the barrel

Now, (c/a)/(desired ratio)

Indidentaly, you can ignore the pi's, because they cancel.

[Fight The Machine]

Thanks for the formula, now I have a grasp on this.

[b-nice]

if your going to spend 15 bucks on a igniter that will fail after 30-40 shots try ordering a stungun and look in the how-tos to see how to work it into your gun. that is what i did cause over the period of the last 8-10 years ive spent countless dollars at lowes on bbq ignighters.

[CS]

On one of my earliest combustions I installed a grill ignitor Ive had it for a year and half. I shot it almost daily I leave it on my porch and never bring it inside suns been shining on it every day. And every once and a while it gets rained on. Screws on the inside are rusted and guess what it still works! I dont know what everybody is doing wrong but with this grill ignitor ive got at least 500 shots maybe even a 1000 shots. Never once have had to tinker with it. I bought it from wal mart so I sure its nothing high tech.

[taterjim]

I have experimented with different barrel lenghts and combustion chambers from 1 ft to 2 ft and in between , I have tried 2.3, and 4 ft barrels and the 3 ft barrel always seem to outperform with my cannons.

My latest igniter is a torch lighter I purchased at an Atwoods store for 7.99 . It looks similar to a barbecue lighter but it has a steel tube instead of plastic and no threads . The top part of it is about the same as the bbq igniter. To install it I drilled a hole in the 4" clean out plug ( center) for a tight fit and on the inside I filled it with hot glue in the square recessed area, It works really well and dependable. I also have a flint lighter in a cap . It works well but isn't as much fun and the flints don't last long. The brass tube seems to wear quickly leaving you with air leaks. I like to push t he spud in about an inch , put in the fuel and then push the spud down to the chamber and compress the mix for a really good shot , I like to see that spud go plumb out of site. I also shoot those toy balls that cats play with ,,the lighter ones don't go up but about a hundred ft or so and just kind of float down , the heavier ones which I assume have a lot more rubber in them willl go out of sight and finally come back into focus ,but every once in a while they go up and you never see it again, my neighbor down the road was kind enough to bring me one back yesterday.