Hi, guys,
New_comer has it almost reversed. Blowback operated firearms operate solely from the pressure in the cartridge case. In one direction, it pushes the bullet out of the barrel, in the other direction it pushes the fired case back against the breechblock. In a pure blowback, only the mass of the breechblock keeps the breech closed until pressure drops enough to prevent the case from being blown apart. It is also this mass that keeps the slide from moving as fast as the bullet; if the slide weighed the same as the bullet, it would move as fast and (barring some stop) as far.
In a recoil-operated locked breech system, the type used in most higher power pistols, it is the recoil from the bullet's forward movement that drives the barrel and breechblock, locked together, to the rear. Some mechanism outside the barrel/breechblock unit disconnects the barrel from the breechblock after the pressure has dropped and allows the breechblock to cycle, extracting and ejecting the fired case and, when the recoil spring asserts itself, to pick up a fresh round from the magazine and chamber it. In a recoil operated system the gun will not operate if the bullet does not move; if the barrel is blocked to prevent bullet motion, the gun will not function.
Jim