SpudFiles

for a while now i have been making pneumatic cannons, and have made some pretty powerful ones. But i was getting tired of always having to shoot by my garage where my air compressor is, so i mad a cheep combustion gun and was absolutely amazed at the power of something that small and simple. so i have decided i want to make a propane metered one so i have less stuff to carry around. I am just wondering how big of a chamber i would need to get good power but now use tons or propane, i plan on using a 79 inch long barrel that is 1.5 OD. and a 3 inch chamber, but how long should it be to get MAXIMUM POWER ?

You know, I'm a combustion guy, too. Pneumatics are more powerful and perhaps slightly more reliable, but they're not as portable, and they don't produce muzzle flash

Anyway, for your C:B ratios....

79" long x 1.5" dia barrel = 139 cubic inches (ci).

For a .8:1 ratio (most efficient) you'd want a 3" dia x ~16" long chamber.

For a 1:1 ratio (less efficient, slightly more powerful, and louder) you'd want a 3" x ~20" chamber.

For a 1.5:1 ratio (ineffecient, but powerful and loud as a mother) you'd want a 3" x 29" chamber or a 4" x 16" chamber.

I'd go for a 1:1 ratio, personally.

Don't forget a chamber fan, and ideally, a way to vent the chamber without having to unscrew a cap (a 1.5" or bigger ball valve works excellently for this). Spark strips are a big plus, too. Try to put as few holes in the chamber as absolutely possible.

Hope that helps you.

Peace,
Pete Zaria.

thanks, i think i might go with a 23 inch long peice, cause i already have it cut and no point in cuting 3 inches off it. I do plan on putting a chamber fan and spark strip in it, with a camera flash ignition. so with a 23 inch long peice of 3 inch pipe, what volume should my propane meter be?

hey what about the latke style venting like in gorts blue flame
http://www.spudfiles.com/forums/gorts-b ... t7878.html

edit
and use the fuel tools
http://www.burntlatke.com/calc.html
http://www.spudfiles.com/forums/evbec-a ... t1212.html

23" x 3" = 162ci.

The volume of the propane meter doesn't matter all that much as long as you put the right pressure in the meter.

For a 162ci chamber, you'll want to injet 6.52 ci of propane for a 4% mix.

For a launcher this size, I'd probably build the meter out of 3/8ths" pipe (it's cheap in brass fittings at local hardware stores). So you'd want a meter pipe 9" long (between the valves) at 60psi, or a 1/2" meter pipe 5.2" long at 60psi.

This tool will help you figure it out exactly: http://www.burntlatke.com/ft_live.html

Breech loading, chamber fan, spark strip w/ flash circuit, ball valve vented, propane metered... yep, sounds like a great advanced combustion setup

You're welcome

Peace,
Pete Zaria.

thanks allot, i am not sure about the breach loading thing yet, i have tried it before with little to no success. but i am going shopping for some stuff tonight to i am going to see what i can find, cause breach loading makes things allot easier.

breechloading is easy man if you don't got any breechloaders than your behind, I love making breech devices because the close enough rule comes handy, that rule is way out of question for pneumatic chambers and valves

if you want a simple solid breech system just use cam locks in fact aren't they still on sale at BCARMs

well i cant buy anything online all i have is what i can get intown, speaking of what i got intown, i got all the parts to make a propane metering system 8) i am going to put it togather tomorrow