Abstract: A safety lock is described for weapons in which the safety lock includes a rigid housing 20 enclosing a hammer spring 27 and plunger 28. The plunger 28 receives an end of a hammer pin 34 either supplied with the weapon, or the present lock 19. The hammer pin is received through an opening at the top end of the rigid housing 20 to engage and press axially against the plunger 28. The plunger 28 includes a plunger shaft 31 that extends along the spring axis through the spring to a rotatable cam 37 (62) which may be selectively moved by a lock assembly 47 to shift between a position in which a recess is aligned with the plunger, thereby allowing the plunger to move axially and permit operation of the weapon, or to position a lock surface 40 in alignment with the plunger, for abutting the plunger and successfully locking the plunger in position so the associated hammer pin and hammer may not be operated.