EMPLOYMENT: Nose fuze for 20-mm A.A. projectile with self-destroying arrangement. (See fig. 551.)

Over-all length: 1.062 inches.

Maximum diameter: 0.75 inch.

Threaded length: 0.375 inch.

Number of threads: 8 RH.

ACTION: As the projectile leaves the gun, the rotation imparted to it by the rifling cau-ses the spiral bore safety ribbon to unwind enabling the firing pin to pass on to the pri-mer on impact.

The following is the self-destroying actions: Preparatory to firing, the firing spring bush-ing is under tension because of the firing spring and is held in a cocked position be the firing lever. This lever is held in position by the catch. The centrifugal segment allows the catch to remain in the locking position and prevents the lever from unhooking itself. Should this lever unhook itself the firing spring bushing, because of the firing spring, would force the lever out of position and the firing pin would be shoved through the cen-tral hole stopping on the spiral bore safety ribbon.

Upon firing, centrifugal force causes the centrifugal lever to move outward. This move-ment causes to catch to pivot slightly taking the strain off of the segment. As soon as the segment is set free, it is bent outward because of centrifugal force. Since the metal in the segment is soft, there is no spring action to bring it back to its former position. During flight the lever, because of centrifugal force, continues to hold the catch in the locked position. The mechanism remains in this position as long as centrifugal force can equal the tension created by the spring which tends to release the catch.

As the rotation of the projectile decreases, the centrifugal force accordiingly decreases causing the centrifugal lever to relax its pressure on the catch. The tension of the spring opens the catch which releases the firing lever. The firing spring and bushing, together with centrifugal force, moves the lever outward, allowing the firing spring bushing to pass through the central hole. Since the spiral bore safety ribbon has now completely un-wound, the firing pin will carry through and fire the primer.

Of special note in the mechanism is the highly polished surface of the firing spring bush-ing. This smoothness is probably necessary for the proper functioning of the fuze.

Figure 551 – Z.Zerl.Fg.