the firearm 11 may be displayed when a shot is fired the corresponding casing is expelled via the expulsion window 13 a such that the casing interrupts the continuous infrared signal emitted from the first emitter 31 once the first receiver 32 detects the momentary absence of infrared signal it generates an electrical control signal corresponding to the interruption of the infrared signal received and this is supplied to the microprocessor 33 that increments by one unit not only the score of the number of shots fired by the firearm 11 but also the score of the number of shots fired using the magazine 13 fitted to said weapon consequently the screen 21 of the counter may show visually information selected by the user of the firearm 11 from the various information items that the screen 21 of the counter is able to show such as total number of shots fired number of shots remaining in the current magazine 13 number of shots fired using the current magazine 13 and the like to this end the user of the weapon merely has to select by means of the keyboard 34 the type of information he wishes to see on the screen 21 the counter 12 is located on the upper part of the barrel of the firearm 11 over the expulsion window and such that the display screen 21 can be seen by the user of the firearm 11 when he is about to fire a shot i e the screen 21 faces the user cf fig2 also the first emitter 31 and the first receiver 32 have to be located such that it is guaranteed that the casing when expelled from the cartridge chamber will interrupt the infrared signal in addition the screen 21 may be offset.