Removing the mass of the air from the barrel of a ping-pong ball cannon, and adding 15 psi to 80 (a 19% increase in pressure differential and therefore force)…. is a whole lot difference to removing the mass of air from the barrel of a Texan and increasing the pressure differential by 0.3%....
The launch tube is evacuated to minimize air resistance during acceleration of the projectile.
This thread has been sidetracked there before, please start a thread on light gas guns if you wish to discuss them...
Anyway that video claims barrel vacuuming produces 13.6 times the energy. That's well enough to me to skip the whole statement as BS.
Lloyd's 2162 fps shot used such a system
Still, I got within 70 fps of him with a conventional PCP firing a 1.8 gr. airsoft BB....