Quote:
Originally Posted by swt70611
I have access to tubing. Interior walls are better than pipe and could be smoothed with a hone. What's the magic length?
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I wish I knew more about optimal lengths. We like 4 ft for our combustion designs, but this is our first pneumatic. Most pneumatic designs have 4-6 ft barrels with reservoir volumes ~2 times the volume of the barrel.
If your reservoir volume is the same as your barrel volume, you only have half the original pressure pushing the projectile at the end of the barrel. If your reservoir volume is twice your barrel volume, you have 67% of the original pressure pushing the projectile at the end of the barrel, assuming the ideal gas law applies. Barrel dwell time is 1/20 to 1/10 of a second, so you need to get the valve open and have enough gas move through quickly to maintain that kind of pressure behind the projectile.