Security device for a gyratory projectile presenting a definite axis of gyration parallel to the definite direction of translation of the projectile, comprising a movable organ in the interior of the body of the projectile, at least one securing pin for such movable organ, said pin being movable, under the action of centrifugal force which accompanies the gyration of the projectile, from one position of security of the movable organ in which it cooperates with such organ to immobilize said organ in such one position of security, to a second position, of freedom of the movable organ in which such cooperation between the organ and the pin ceases,
- the said organ being movable in the interior of a cage which is mounted in the body of the projectile for free rotation around the axis of gyration with respect to the body, means mounting the cage so as to permit a play of the cage with respect to the body in a direction parallel to the axis of gyration of the projectile between two abutment faces respectively before and behind the body with reference to the direction of translation of the projectile, whereby the acceleration and the deceleration to which the body is successively subjected respectively during its trajectory in the barrel of the weapon and after the exit of the weapon from the barrel puts the cage and the body respectively in relationship to the driving of the cage by the body by their conjoint gyration by friction of the cage against the rear abutment and in relation by friction of the first by the second by the gyration by friction of the cage against the forward abutment face, with a transitory period corresponding to the passing through the play by the cage during which such last is free from the gyration with respect to the body and turns around the axis of gyration at a speed of gyration which decreases less rapidly than that of the body and is superior to such speed,
- the said pin being mounted to slide radially in the cage in reference to the axis of gyration between on the one hand a position of locking in which its radially inner end more nearly approaches the axis of gyration and cooperates with the mobile organ in the interior of the cage, to immobilize such organ in said definite position with respect to the cage and in which the radially outer end of the pin, the more distant from the axis of gyration lies substantially even with the exterior peripheral face of the cage to form a cylinder of revolution around the axis of gyration, and on the other hand a position of liberation further from the axis of gyration and in which the formerly radially inner end of the pin more closely approaches the free mobile organ, and there is provided at least a spiral elastic band interposed between the external peripheral face of the cage and an inner peripheral face of the body, the mass, the form, the rigidity, and the prestress of the spiral elastic band being such that they are rolled around the external peripheral face of the cage and grip it in such manner as to be become solid by friction with it in repose and such that it sustains, in abutting against the rear abutment of the body upon the acceleration of the projectile in the barrel of the weapon, a conjoint gyration with the body with a speed ranging from the value zero to a maximum value, the spiral elastic band expanding exteriorally to become disengaged from the cage under the action of centrifugal force having a value slightly less than or equal to such maximum value in order to engage the peripheral inner face of the body and become solid with it by friction, whereby during said transitory period and when the cage engages against the forward abutment face of the body in the deceleration of the projectile outside the muzzle of the barrel of the weapon, the difference between respective speeds of gyration of the cage and the body, introduced during said transitory period, provokes a centrifugal unwinding of the spiral elastic band with the liberation of the pin or pins in the direction of a movement of unlocking of the mobile organ to a position of liberation thereof.