How does a blowback-operated firearm cycle after a round is fired?

In simple blowback operation, the firearm cycles by utilizing the energy generated from the explosion of the cartridge. When a round is fired, the pressure forces the empty cartridge case backward. This rearward movement pushes against the bolt, or breechblock, forcing it to move backward as well.

As the bolt travels rearward, it compresses a spring. This motion is responsible for the mechanical cycle of the weapon, which includes the extraction and ejection of the spent casing. Once the bolt has reached its rearward limit, the compressed spring expands, pushing the bolt forward again to return it to the firing position, typically chambering a new round in the process. The primary challenge in this design is managing the rearward velocity of the bolt to ensure the cycle of loading, firing, and ejection occurs reliably.1