The invention relates to mechanisms for cocking an automatic weapon. An automatic firearm having an inertial automation system comprises a breech, a barrel, a bolt support with a bolt, a recoil spring and a return spring, a trigger mechanism, an ammunition supply mechanism and a bolt support latch. The latch fixes the bolt support in a rear position and is controlled with a trigger. A shot is produced at the instant the bolt support arrives in a front position. A mechanism for supplying cartridges to a cartridge chamber makes it possible to load the weapon when the bolt support is fixed in the rear position. Stable operation of an inertial automation system is achieved.