If any of you have wondered if it is possible to shoot > Mach 1 with a butane gun, I found the answer a few months ago: It is.
The gun is made of unrated PVC pipe (somehow I'm still alive, but rated pipe is just too hard to get by in Denmark -- nobody does DIY plastic plumbing).
The chamber is 105 cm long, 110 mm in diameter (a long and narrow thin-walled pipe will withstand more pressure than a short and chubby one, for the same volume). The sparker has 4 gaps, evenly spaced. There is a PC fan at the breech end.
The barrel is 5 meters of 50mm OD pipe. I did some calculations, and found out that with the reletively low pressure of a combustion gun, a barrel of this length was needed.
With a perfect air/propane/butane mix, it would shoot about 280 m/s with a light plastic ball.
With about 40% oxygen in the chamber and a double gas charge, the ball comes out with at least 380 m/s (Mach 1.13) (I put a magnet in the ball and shot it through two electromagnetic coils, starting and stopping a microsecond timer. The coils were 75 cm apart, measuring _before_ the muzzle. At the muzzle, the velocity is yet a little higher).
Sonic booms are LOUD, even for small plastic balls
Safety mesaures included hanging heavy rugs over the chamber, and firing the thing from a gooood distance.
Next thing must be to find out if it can launch a potato at those speeds as well. It will require more pressure, that means, more oxygen and more fuel in a better chamber.
Good fun it was anyway.
Søren
. Also I dont think you woul dget to many shots out of it, because the pipe might start to weaken over time..Stay safe! Peace!
) If it blows up, well, there is only one sound barrier and it has broken it.
