referring now to the drawings , reference character 1 generally designates one of the two hammers of an &# 34 ; over - under &# 34 ; double - barrel shotgun or a &# 34 ; side - by - side &# 34 ; double - barrel shotgun , the hammers being pivoted on the underguard 2 by means of a transverse pin 3 , so as to be angularly displaced to and from their respective striker 4 and guided in a manner known per se and conventional within the body of the lever 5 of the shotgun . the hammer 1 has , on its rearwardly facing surface and at an intermediate height , a step - like portion 1 &# 39 ; on which there are located two trip teeth 6 , 7 , one positionally following the other and positioned in a plane which is above the axis or pivoting axis of the hammer 1 when the hammer 1 is in the released position , such as shown for example in fig2 . one of the teeth , for example tooth 6 , is so constructed as to define the arming position of the hammer 1 while the other tooth 7 constitutes the means for safety - positioning the hammer 1 as described later hereinbelow . the hammer 1 has associated therewith a respective trip lever 8 pivoted on the underguard 2 by means of a pin 9 and having a first portion 10 and a second portion 12 . the first portion 10 , substantially horizontal in the armed position faces and cooperates with a trigger 11 in a manner known per se ; the second portion 12 , directed upwardly and positioned behind the hammer 1 , has a frontwardly facing projection 13 which engages , alternately , one or the other of the teeth 6 , 7 of the hammer 1 . the trip lever 8 is in turn urged by a compression spring 8 &# 39 ;, which acts upwardly in a substantially vertical direction between the underguard 2 and the trip lever 8 , so as to keep the portion 12 thereof constantly adjacent the hammer 1 . the trip lever spring 8 &# 39 ; is interchangeable so as to allow the desired variation of the force applied to the hammer 1 by the trip lever 8 . the position of the arresting teeth 6 , 7 with respect to the pin 3 allows the obtainment of a lever arm of such length as to affect and favorably influence the ease and smoothness of the operation for a more correct and precise utilization of the firearm . furthermore , while the tooth 6 allows the blocking of the hammer 1 in the correct armed position , which is achievable by means of a full opening of the barrels , the tooth 7 serves to arrest the hammer 1 in the event of an incomplete arming of the hammer 1 caused by a partial opening of the barrels . in this case , in fact , the projection 13 of the trip lever 8 engages the tooth 7 and insures the blockage of the hammer 1 so as to prevent the uncontrolled or accidental action of the striker 4 and the corresponding firing of the cartridge . furthermore , the tooth 7 also serves as engagement means with the trip lever 8 , when tooth 6 is worn and there is no possibility of a sure engagement of the projection 13 of the trip lever 8 with the arresting tooth 6 . there is , therefore , achieved a greater safety in the operation of the mechanism and , consequently , the elimination of any possible uncontrolled or accidental release of the hammer 1 . according to another feature of the invention , each hammer 1 is associated with a trip spring 14 of predeterminedly regulated load so as not to affect the hammer 1 when the latter is in a rest position , ( hammer 1 already released ), and so as to keep it free and disengaged from the striker 4 . to this end , the spring 14 is mounted on on a guide rod 15 and is arrested with a pre - load between a striking collar 16 provided in the vicinity of one of the terminals of the guide rod and an internally threaded regulating sleeve 17 threaded onto the opposite extremity or terminal of the guide rod 15 . furthermore , while the threaded extremity of the rod 15 is guided within an opening provided in a ring 18 of the support 2 &# 39 ; of the underguard 2 , the opposed extremity of the guide rod 15 is provided with a hemispheric - shaped head 19 and is lodged in a seat 20 provided in the rear part of the hammer 1 . the pre - loading of the spring 14 is regulated by threading or unthreading the regulating sleeve 17 as desired , on the guide rod 15 . in any case , the maximum extension or length of the spring is limited by the regulating sleeve 17 with the striking collar 16 provided on the guide rod 15 , the extension or length being a function of the distance of the hammer 1 from the confronting surface of the ring 18 and of the freedom which the hammer 1 must have when disarmed . however , the regulating sleeve 17 , as well as the guiding opening in the ring 18 , have a diameter smaller than that of the spring 14 , so as to force the spring 14 to rest against the ring 18 while the guide rod 15 is displaced axially within the opening during the arming and disarming operations . in this manner , when the hammer 1 is moved into the armed position ( fig1 ) the spring 14 is compressed and is therefore &# 34 ; loaded &# 34 ; between the collar 16 of the guide rod 15 and the guiding ring 18 . by the subsequent releasing of the hammer 1 , the reaction of the spring 14 is unloaded on the guide rod 15 which then forcibly moves the hammer 1 itself toward the striker 4 for the firing thereof . however , when the spring 14 has reached its maximum extension , defined as described above by the regulating sleeve 17 and by the collar 16 , the hammer 1 is not affected and is free to effect slight angular displacements , thus permitting the full return of the striker 4 to a resting position . the rubbing action of the striker head 4 against the bottom of the shell casing and against the breech of the barrels when these are being opened is thus completely avoided .