14.7psi (1 atmosphere). The main principal is that inside the barrel, in vacuum, the projectile encounters near zero resistance so it can accelerate at an insane rate. It's traveling Mach 3+ in the barrel but slows to a meezly ~400mph the moment it comes out the end and hits air!
Don't have any sort of throw bag launcher design in the works yet or anything but I have been thinking about it...
Look up Smarter Every Days video "how hard can you hit a golf ball", of course Destin takes it to the absolute extreme limits (him and his buddy in the video are literally rocket scientists) but he explains all the science behind how it works and stuff too.
