The “Stogers World Fair Edition Catalog” for 1939 lists both Britishicon and Germanicon (DWM) ballistics data. The British data is expressed in the familiar ‘foot-pound-second’ (fps) system while the German data is expressed in the metric ‘centimeter-gram-second' (cgs) system. Both Hatchers Notebook and Stogers list the conversion factor from grams to grains as 15.432. Since the bullet data lists the weight as 16.7 g (grams) there is no reason to use a conversion factor with any more precision than 15.4. Therefored the 9.3 mm bullet weight is probably close to:
16.7 g(Grams) x 15.4 = ~ 257 GRAINS.
Hope this helps.