the invention fig5 and 6 respectively show a longitudinal section view with respect to an a a plane and a plan view of a firearm 11 wherein a preferred embodiment of actuator means 10 according to the present invention is installed and the assembly in which said actuator means 10 interact with the firearm 11 mechanism furthermore fig5 a 5 d show a first embodiment of actuator means 10 in the different operation positions firearm 11 comprises a percussion member 16 or cane suitable to hit the projectile arriving from a loader 17 inserted within handle 12 in order to permit switching on of propellant charge said percussion member 16 can be operated by a suitable mechanism connected by a motion transfer lever 18 pivoted on trigger 13 u2032 pin 18 u2032 which is pivoted on the firearm by pin 13 u2032 when the trigger 12 is pushed up to the end lever 18 moves according to direction a thus freeing percussion member 16 suitably preloaded making the shot firing in an embodiment said actuator means 10 comprise an electric engine 19 with a shaft 20 keyed on a worm screw 21 threading of which is engaged by a mating thread of a threaded channel of a body 22 said motor 19 is housed within the bottom part of the trigger 13 of said firearm 11 so that stresses applied on the trigger 13 are not transmitted to the movable parts and to the cage of the same motor 19 furthermore said lever 18 has at the bottom an offset 23 in which can be engaged the upper part or head.