Manual

5.1.3. Unlocking and recoil of bolt
The gas pressure, generated by the burning powder, drives the bullet
up the barrel [13]. As soon as the projectile passes the gas port [15],
the propellant gas flows through the adjustable gas valve [14]. The gas
pressure acts on the gas piston [1] which pushes the bolt carrier to the
rear.
Bolt carrier recoil begins
49