Improvements introduced in a firearm of automatic loading that has a frame, a gun attached to the frame, a closure mounted for longitudinal movement in the frame behind the barrel, an automatic loading mechanism connected to the closure to move the closure from its position closed in front of its open rear position and return when firing the firearm, a hammer pivotally mounted in the frame, said hammer being formed with a main detent notch and with a secondary detent notch, a trigger pivotally mounted in the frame, said trigger having a main latch for engagement with the main detent notch of the hammer, a secondary latch pivotally mounted on the frame to engage with the secondary latch notch of the hammer, a rocker arm pivotally mounted on the frame, the rear end of the rocker arm being pivoted upwards when the closure is in its closed front position and being moved downwardly when the closure is moved to its open rear position, by making said upward and downward movement of the rocker arm, in turn, that the secondary latch disengage from the secondary latch notch of the latch. Hammer and allowing the secondary sear to engage in the secondary detent notch of the hammer, whose improvements comprise a firing mechanism capable of firing semiautomatically, in a fully automatic mode and in bursts of predetermined duration, said mechanisms comprising a switch support member and disengaging the secondary latch pivotally mounted on the frame, by moving upwardly of the forward end of said pivoted bearing member that the upper end of the secondary latch moves back out of engagement with the secondary latch notch of the hammer; a switch and orientation assembly mounted for rotation at the forward end of said support member, said assembly comprising an orientation pawl having a predetermined number of ratchet teeth and a switch disk having at least one arm contact surface of disengagement and at least one notch to receive the release arm; an orientation finger pivotally mounted on the hammer, said finger engaging the teeth of said orientation pawl and causing said switch and orientation assembly to rotate one tooth each time a cartridge is fired; a positioning element in position of the activating lever pivotally mounted in the frame for longitudinal movement to a more delayed position, to an intermediate position and to a more advanced position; an automatic trigger activating lever pivotally mounted on said positioning element in position of the activating lever, said activating lever having application means with the rocker arm intended to be applied to the rear end of said rocker arm and a release arm of the secondary sear destined to make contact with the switch disk of the switch and orientation assembly, said means of application being with the rocker arm and said release arm of the secondary sear being movable forwards and backwards by the corresponding movement of the positioning element in position of the activating lever and being movable up and down by the corresponding movement of said rocker arm when in application therewith, said unlocking arm of the secondary sear moving to the forward end of said support member upwards to unhook said fiad or secondary when said disengage arm moves forward and upwardly in contact with a contact surface with the arm, of said switch disc; said positioning element being moved in position of the activating lever to its most backward position to put the activating lever in its semiautomatic firing position, in which the application means with the rocker arm are out of application with the rear end of the rocker arm, and the release arm is out of position to make contact with the switch disk of the switch and orientation assembly; said positioning element being moved in position of the activating lever to its intermediate position to place the activating lever in its burst firing position, in which the application means with the rocker arm are in application with the rear end of the arm of the rocker arm, and the forward end of the release arm is in position to make contact with the contact surfaces with the arm and to enter the notches to receive the arm of the switch disc when the release arm is caused to move upwards by the rocker arm; and said positioning element being moved in position of the activating lever to its most advanced position to place the activating intermediate lever in its fully automatic firing position, in which the application means with the rocker arm are in application with the end the rear of the rocker arm, and the forward end of the release arm are in position to make contact with the contact surfaces with the arm of the switch disc and is ahead of the position in which it can enter the notches to receive the arm, of the switch disc when the release arm is made to move upwards by means of the rocker arm. (Machine-translation by Google Translate, not legally binding)