Morter Sub-Projectile?

Does anyone know what this is? My guess is some kind of Morter Simulator. It is 138.36mm (5.447 inches) long. the head is 25.16mm (0.991 inch) in diameter. The main body is 20.32mm (0.800 inch) in diameter. Both the head and tail stock unscrew from the body. The head has a hole through it. There are no markings of any kind.