jeepkahn wrote:I was refering to the fact that ggdt undershot the heavy balls, and overshot the light(due to gas terminal velocity in the barrel)....
Maybe one of you gas dynamics experts can answer a question of expanding gas in a cylinder....
If you open the end of the cylinder does the gas expand like a sweater unraveling, or does it expand like a spring???
It depends on the pressure. At low pressure like a balloon pop, it is like a spring. The air mass has little affect. At high pressure with supersonic flow, it is a mix of both, like a line of cars taking off at a traffic light, but the rear impatient to get rolling. Air mass and the wave of pressure release has a high enough amplitude transversing the cylinder to set up pressure gradient waves. The pop echo has an effect on the pressure over time as it travels the cylinder. This is why a short fat cylinder is considered better than a long one for supersonic attempts. More air is already in the vicinity of the valve and needs less acceleration to reach the entrance of the valve when the fast valve opens.
It is why the chicken cannon has a shorter fat chamber.
A competing school of thought is a long chamber will accelerate the flow before the valve. The thought is good but ignores the flow resistance in a smaller pipe and the effects of transonic flow or supersonic flow in the valve. Air arriving at the valve arrives at higher speed, but lower pressure.. Pressure and compression will make it obvious that the volume of air reaching the valve is BIGGER in volume as it arrives at a LOWER pressure. This contributes to a slower terminal velocity as the lower pressure chunk of air is bulkier and has to take more time to get it all through the valve into the barrel.
It is better to get the bulk of the HIGH pressure air through the valve quickly and let the expansion take place in the barrel where it will do the most good.
I hope this somewhat non technical and totally absent of math description helps.
Dear god... 
