The attached picture shows an AP projectile which has come out of an unheadstamped brass 20 x 138 mm case. There are no stampings or markings on the body of the shot/shell? The rear of the projectile beneath the driving band appears to be screw threaded and in the inset you can see two keyways cut out of the base. I have tried to gently unscrew the base but cannot do so. The item needs to be certified as Free From Explosive. Does anyone know the construction of the projectile and what sits beneath the base? In addition what nationality is it?
Thanks in advance.