Ryan, I am afraid you are wrong.
Pressure, if given a chance, will equalize, however, as the projectile moves down the tube the fluid dynamics becomes very complicated, in fact, high powered air cannons often are found to work just as well as lower pressures because the air simply doesn't move fast enough for 100 psi to create any more pressure once the projectile starts moving than, say, 25.
Go weigh some darts, then check back in. .625 caliber darts actually do weigh more than 2.44 times as much as the .40 caliber ones, especially if you're comparing "hunting" quality ones. 2.44 times as much force on
more than 2.44 times as much weight, means a slower dart with more force.
The lungs are only capable of 5 or 10 PSI, but several gallons of volume. In the context of airguns, that
does mean continuous pressure for any reasonable caliber airgun. Human lungs are
nothing like a precharged airgun. They're really more like CO2, which is fixed at about 800 PSI, until the cartridge runs low.
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Please don't let this degrade into a debate about your personal interpritation of physics.
Okay, this statement is
exactly what's wrong with the education system these days. There is no
personal interpretation of physics. Physics work the way they work. Air works the way it works. And it's a very simple fact that you cannot blow 5 PSIg into
any bizarre shape of magical tube, and somehow end up with more than 5 PSIg
anywhere in the system. If the public education system had done its job properly, you would know that a magical "force multiplier" like that would
literally allow for a first-order perpetual motion machine, which draws infinite energy out of the aether.