hello 'M', thanks for responding, unfortunately there are no ink markings on the shell body, the screw in tracer sits on the steel disc, under the disc is "lead" , the total weight is 147g with tracer , length of projectile minus the tracer unit is 79.6mm, having gone through my books and paperwork I eventually came to the same as you, AP-T inert filled and due to the weight i am assuming it is for the 2cm flak 20x138B cartridge
Mick