SpudFiles

Well I was building a golfball launching combustion unit, It took me forever to find some 1.5" SDR-21 and the 2" sch80 to sleeve it in. The SDR-21 the gave me for free(it was scrap) but I had to by the 2" and that was a bit expensive, So I didn't buy and pipe for the chamber as I remembered I had some 3" that I had from putting in a drain. So I get home and low and belond the 3" is DWV not pressure tested. grr But while looking through my shed I found a propane (5gallon, 25lb) bottle that I had taken the valve off and used as a counterweight for my catupult, I dug around and found a 2" castiron pipe nipple I'm going to cut out around the valve and weld in the the 2" cast iron to the tank and I'll put a 2" threaded(female) on the barrel.
Think the LP tank will work as a combution chamber?

No reason why not,aslong as you have a big barrel to keep the ratio healthy other wize expect some eardrum shattering shots.

The only problem I see is that the metal propane tank conducts electricity, which means you'll have to insulate your electrodes from the tank. Easiest way to do this would, in my opinion, be a spark strip. http://www.burntlatke.com/strip.html .

As rna_duelers pointed out, you'll need a pretty long barrel to keep a decent chamber:barrel ratio.

Peace,
Pete Zaria.

I have a 4 foot golfball, and a 7 foot section of plain old 2". Which would you think would be better? and is there any caluations for barrel to chamber ratio?