/sci/ - Science & Math

There are these pistols that use a system called gas-delayed blowback.
As seen in the picture, there is a little port on the underside of the barrel that bleeds the expanding gases from the explosion into a separate chamber beneath the barrel.
Supposedly there is much more heat and pressure in the chamber than there is in the barrel.

Why is this? Why doesn't the high pressure gases that have been leaked in the chamber go back to the barrel to equalize the pressure?