This one is allegedly an incendiary loading that was manufactured prior to WW2 when the Germans starting playing around again with the rifle calibre anti-tank rounds culminating in the 13 x 94 (PzB38)and 7.9 x 94 (PzB39).
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The post 1918 production is not related to AT rifles and also not to the 7.92x94. These cartridges were for aircraft machine guns and were a competitor to the 13x64B which got finally adopted.