SpudFiles

I first read that 1.5 to 1 is optimal so that is what I designed for. It was OK but when I switched to metered propane and a combustion the gun sounded like a shotgun. Recently I emailed someone who said I should try for .7 then refered me to this site. I seen his impressive videos but if I were to design for .7 then my barrel would be 9 feet long. Any advice? I have a 3" chamber that's about 115 cubic inches and my barrel is about 34" @ 1 1/2 dia.

If you want the best of both (i.e. sound and portability + efficiency and power) why don't you just make a few different barrels? Also, you could use a 2" barrel, which wouldn't need to be as long to achieve a more powerful ratio.

Also, this probably belongs in the combustion cannon discussion, as it is specifically related to combustions.

i use a 4"x24" chamber and a 1.5"x6.5' barrel and i love it but i would suggest useing a camlock system for interchangeable barrels

Well, I guess I can always go to 2". I didn't install a camlock but I can remove it easily. Another projectile I wanted to launch is tennis balls and thats a 2.5 barrel.

Has anyone ever tried to extend their combustion chamber? I think I can add volume by adding a threaded adapter, a length of pipe, and a cleanout. Has anyone tried this? I guess I'll let you know.