US Cartridge, 37mm Dummy, M21
This completely inert cartridge simulates service HE cartridge M54 and is used for training in handling, loading and firing.
The dummy cartridge consists of steel cartridge case M17B1 assembled with a modified empty projectile and dummy fuze. The projectile and case are held together by a steel retaining rod, one end of which is inserted into the enlarged tracer cavity in the base of the projectile. The other end is screwed into a cartridge case plug assembly which takes the place of the primer. This plug assembly forms a free fit in the primer hole. A copper plug is assembled in the base of the plug assembly so that the firing pin of the weapon will not be damaged in simulated firings.