...dictate that be the case. For example, consider that, after the piston has moved half the length of the stroke, the compression ratio is only 2:1, producing only about 20-odd psi behind the pellet. That's only about 1/10 of the pressure required to force the pellet to overcome friction and start moving. At the 3/4 point, the pressure is still only ~90psig - still not enough to budge the pellet.
But theory aside, many folks have verified the fact experimentally, including the Cardews (as set forth in "...Trigger to Target"
) and our own Mike Adams with his accelerometer experments.
This demo summarizes the findings.