As the piston move closer to the cylinder head it picks-up speed and reaches it's maximum speed just before it completes it's stroke.
This is another aspect that I have a hard time with, as I can at least attempt to reason the possibility of this being both true and false.
The part of me that thinks it could be true has to do with resistance, but how much resistance does a 6mm opening with a .2g BB in it really cause compared to the relatively massive tension of the spring? Is it even going to be noticeable? Working on airsoft replicas gives me a false impression about the actual resistance involved, as my thumb isn't going to move, which is the purpose of using it to test compression anyway.
The part of me that thinks this claim might be bogus, has to do with the tension of the spring being exponentially reduced during the motion of the piston. And while my tentative understanding of inertia suggests that the piston may not significantly lose speed--if at all--I don't see the logic behind it
gaining speed even after whatever resistance of the BB/inner barrel is overcome, because the energy being provided isn't being increased and I don't see it taking any measurable time to reach peak velocity given the seemingly meager mass of all the objects involved.
Someone needs to set up a microphone and recording software to see if the point the piston is released is distinctly audible (or visible on a waveform), and then measure the difference between the two cylinders in milliseconds. I think that would be the clearest way to measure it considering we both have different hypotheses about which variables have a bigger impact on the BBs velocity. Rate of fire won't work accurately either, because of the fluctuations in voltage of the airsoft batteries and draw from the motor. The more isolated we can keep the independent variable (the cylinder), the better.
If the speed of the pistons are the same,
but the velocity is higher in the replica without a port, it would suggest I was right about the increased compression ratio increasing velocity--this could actually be true even if it the piston were to move slower.
If the speed of the piston with a port is greater
and results in a higher fps than the other replica, it lends credence to your hypothesis.
Who knows, maybe there will be a distinctive pitch change during each pistons course that will help us determine when it reaches maximum velocity. That's probably wishful thinking, though. I can't really think of a way to validate or refute the claim I quoted with experimentation, save clear cylinders and high speed video.
This is truly a job for Mythbusters--either that or maybe Fasteen can come out and put us in our places,
argumentum ad verecundiam aside. :P
Anyway DMitry, keep poking away. I think it's a good thing. I think we all would like to know the nitty gritty details that would squarely put this to rest.
Spoken like a true scientist.
Albert Einstein wrote:If we knew what it was we were doing, it would not be called research, would it?