been observed that the invention achieves the intended aim and objects by providing a device which allows optimum operation of the firearm with any type of cartridge the invention is extremely advantageous in application to inertial firearms and to the other types of automatic firearms the auxiliary resilient member acts only if powerful cartridges are used so as to provide an additional thrust to the bolt assembly during the closure step which would otherwise be too slow the auxiliary resilient member also effectively reduces the effects of recoil on the shoulder of the gunner significantly improving shooting performance the device according to the invention is susceptible to numerous modifications and variations all of which are within the scope of the inventive concept all the details may furthermore be replaced with technically equivalent elements fig4 to 6 for example illustrate a device 101 applied to a semiautomatic rifle which is provided with a front recoil spring 3 i e with a recoil spring located in front of the bolt assembly and coaxial to the cartridge magazine 130 the bolt assembly 16 is connected to a sleeve 111 by means of a pair of brackets 114 the recoil spring 3 is operatively connected to the sleeve 111 in such a manner that it is deformed during the backward motion of the bolt assembly as shown in fig5 the sleeve 111 comprises an auxiliary resilient member advantageously constituted by a second cylindrical helical spring 121 arranged between an abutment 117 defined in the sleeve 111 and a ring 125 ring 125 is coaxial to the sleeve and can slide thereon similarly to the preceding case if a weak.