Why two compression chambers?

[jerb]

I've been looking around here and have found a number of guns that feature two compression chambers. I understand that this increases the volume of compressed air the gun can hold but how could you use that extra pressure effectively?

[pneumaNINJA]

For one, you could use a larger barrel, as there is less restriction on air flow, or secondly a valve such as a piston or burst disk allow air to flow more effeciently.

[SpudStuff]

building multiple small valves is easier and more effective than building one large one. also if you double the size of the chamber you can double the size of the barrel which means more velocity

[jerb]

ah, that explaination makes a lot of sense, I didn't consider that

[boilingleadbath]

You <i>could</i> lengthen the barrel, but that's not really relevent to the question.

The real reason is that there is less pressure loss during the firing cycle, so the average pressure is higher, and thus the average force is higher... which generates higher velocities.

For example, let's say your C:B ratio is 2:1 in the single-chambered gun. Simplifing things, if you start off at 100 PSI you will end up at ~43 psi.
With a C:B ratio of 4:1, the end pressure is ~72 psi.

The simplification was that I assumed air to be an ideal gas undergoing abdiatic expansion - effects which would tend to make the difference in pressures more extream.